Add process and network utilities, webhook functionality, and Zig dow…

…nload script

- Implement process information retrieval in `process.zig`, including functions to get executable paths, command lines, UID/GID, and compute executable hashes.
- Introduce utility functions in `util.zig` for parsing IP addresses, ports, and socket states, along with helper functions for string manipulation and filtering.
- Create `webhook.zig` to handle ECS event creation from diffs, serialize events to JSON, and send them via webhook with HMAC authentication.
- Add a script `download.sh` for downloading and installing Zig with support for different OS and architectures.
- Include tests for process info parsing, hash formatting, process running checks, parent PID lookup, ECS event creation, JSON serialization, and webhook config validation.