[extension/encoding/textencoding] Marshaling and Unmarshaling Separator configurations are ignored by the extension

### Component(s)

extension/encoding/textencoding

### What happened?

## Description

The `text_encoding` extension exposes configuration options for `marshaling_separator` and `unmarshaling_separator`. However, these settings do not appear to affect the exported output when used in combination with the `fileexporter`.

On reviewing the implementation in `extension/encoding/textencodingextension/extension.go`, it seems that the configured values for `marshaling_separator` and `unmarshaling_separator` are never applied when creating the `textLogCodec` instance. As a result, the `marshaling_separator` always defaults to an empty string, regardless of the user-provided configuration.

In addition, the current logic in `MarshalLogs()` (`extension/encoding/textencodingextension/text.go`) appends the separator after every log record. This behavior introduces trailing separators (e.g., empty lines when `marshaling_separator="\n"`) instead of joining records in the same way as a standard delimiter would (e.g., `"\n".join(records)`).

## Steps to Reproduce

1. Configure a `filelog` receiver to read logs from a file.
2. Configure a `fileexporter` with `text_encoding` and set `marshaling_separator` to `"\n"`.
3. Observe the exported log file.

## Expected Result

The following should be the expected log output written by `fileexporter`.

```console
<ip_address> - - [19/Sep/2025:10:04:06 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"
<ip_address> - - [19/Sep/2025:10:04:06 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"
<ip_address> - - [19/Sep/2025:10:04:06 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"
<ip_address> - - [19/Sep/2025:10:04:06 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"
<ip_address> - - [19/Sep/2025:10:04:06 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"
<ip_address> - - [19/Sep/2025:10:04:07 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"
<ip_address> - - [19/Sep/2025:10:04:07 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"
<ip_address> - - [19/Sep/2025:10:04:07 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"
<ip_address> - - [19/Sep/2025:10:04:07 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"
<ip_address> - - [19/Sep/2025:10:04:07 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"
<ip_address> - - [19/Sep/2025:10:04:07 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"
<ip_address> - - [19/Sep/2025:10:04:07 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"
```

## Actual Result

1. Configured `marshaling_separator` value is ignored resulting in log lines within a `ResourceLog` getting concatenated together.

  ```console
  <ip_address> - - [19/Sep/2025:10:04:06 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"<ip_address> - - [19/Sep/2025:10:04:06 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"
  <ip_address> - - [19/Sep/2025:10:04:06 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"
  <ip_address> - - [19/Sep/2025:10:04:06 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"<ip_address> - - [19/Sep/2025:10:04:06 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"
  <ip_address> - - [19/Sep/2025:10:04:07 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"
  <ip_address> - - [19/Sep/2025:10:04:07 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"
  <ip_address> - - [19/Sep/2025:10:04:07 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"<ip_address> - - [19/Sep/2025:10:04:07 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"
  <ip_address> - - [19/Sep/2025:10:04:07 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"<ip_address> - - [19/Sep/2025:10:04:07 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"
  <ip_address> - - [19/Sep/2025:10:04:07 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"
  ```

2. When configured properly, the separator is appended after each record, resulting in extra blank lines in the output when using newline separator for marshaling.

```console
<ip_address> - - [19/Sep/2025:10:04:07 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"
<ip_address> - - [19/Sep/2025:10:04:07 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"

<ip_address> - - [19/Sep/2025:10:04:07 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"

<ip_address> - - [19/Sep/2025:10:04:07 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"
<ip_address> - - [19/Sep/2025:10:04:07 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"
<ip_address> - - [19/Sep/2025:10:04:07 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"

<ip_address> - - [19/Sep/2025:10:04:07 +0000] "POST /api/v1/service/log HTTP/1.1" 200 13 "-" "LuaSocket 3.0.0"
...
```

### Collector version

0.135.0

### Environment information

## Environment

OS: Debian 11


### OpenTelemetry Collector configuration

```yaml
# Sample Otelcol configs

receivers:
  filelog:
    include:
      - /var/log/nginx/access.log
    start_at: end
    include_file_path: true
    include_file_name: false

    resource:
      environment: development
      component: nginx

    operators:
      - type: move
        from: attributes["log.file.path"]
        to: resource["path"]
      - type: add
        field: resource.log_path
        value: EXPR(join([resource.environment,resource.component], "-") + resource.path)

processors:
  batch:
    send_batch_size: 8192
    timeout: 200ms
    send_batch_max_size: 0

  memory_limiter:
    check_interval: 5s
    limit_percentage: 75
    spike_limit_percentage: 10

exporters:
  file:
    path: /var/log/otelcol/*.log
    rotation:
      max_megabytes: 5000
      max_days: 7
      max_backups: 4
      localtime: false
    encoding: text_encoding/utf8
    group_by:
      enabled: true
      resource_attribute: log_path

extensions:
  text_encoding/utf8:
    encoding: utf8
    marshaling_separator: "\n"

service:
  extensions: [text_encoding/utf8]
  pipelines:
    logs:
      receivers: [filelog]
      processors: [memory_limiter,batch]
      exporters: [file]
```

### Log output

```shell

```

### Additional context

Only checked the `MarshalLogs()` logic. The logic used in `UnmarshalLogs()` was not checked for correctness. 

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[extension/encoding/textencoding] Marshaling and Unmarshaling Separator configurations are ignored by the extension #42797

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[extension/encoding/textencoding] Marshaling and Unmarshaling Separator configurations are ignored by the extension #42797

Description

Component(s)

What happened?

Description

Steps to Reproduce

Expected Result

Actual Result

Collector version

Environment information

Environment

OpenTelemetry Collector configuration

Log output

Additional context

Tip

Metadata

Metadata

Assignees

Labels

Type

Projects

Milestone

Relationships

Development

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