Fix: extends handling in config files (global + suite)

Fixes #6872

Problem

• extends was expanded too late in the load process:
  • Defaults were merged into the “inherited” config before extends was resolved.
    → Result: scalar values from parent configs were lost (arrays still merged).
  • params from parent configs were ignored (see also #6799).
• For suite configs, extends resolution was missing completely for .suite.dist.yml files.
  → Result: extends in suite dist configs was silently ignored.

Fix

• Moved extends expansion into getConfFromContents(), which is used for both global and suite config resolution.
• Now an entire chain of inheritance is expanded immediately when a config is loaded from file.
• Only after expansion, the normal config merge order applies:
  codeception.dist.yml → codeception.yml → acceptance.suite.dist.yml → acceptance.suite.yml
• Added check for circular extends references with a clear error message.

Result

• Scalars and arrays from parent configs are inherited correctly.
• params from base configs are preserved.
• extends works in .suite.dist.yml files (not ignored anymore).
• Behavior is now consistent across global and suite configs.

Notes

• This matches what the docs currently say about extends.
• If merged, docs might be updated to clarify that the full inheritance chain is expanded first, then the normal config precedence rules apply.