proposal: allow injecting a custom logger (replace hard-coded logrus)

[ilCollez]

Summary

compose-go currently logs internally via logrus with no public switch to:

• silence the output
• redirect it to another sink
• integrate with the host application’s structured logger

This proposal asks to make the logger pluggable (e.g. via a WithLogger option) so that consumers can supply any backend (log/slog, Zap, Zerolog, logrus, etc).

I’m volunteering to do the implementation and open a PR once the maintainers are happy with the direction.

What I’m proposing

• Accept either a *slog.Logger or a slog.Handler through a simple opt-in API:

  func WithLogger(l *slog.Logger)
  func WithHandler(h slog.Handler)

• Keep the current logrus instance as the default handler to preserve existing behavior.
• Users who rely on other backends can plug them through existing adapters:
  • Zerolog: https://github.com/samber/slog-zerolog
  • Zap: https://github.com/samber/slog-zap
  • Logrus: https://github.com/samber/slog-logrus

Notes

• cli.ProjectOptions and loader.Options are plain structs, so adding a Logger / Handler field is straightforward - the caller just sets it via WithLogger/WithHandler.
• Many helpers call the global log instance directly. This causes unavoidable side-effects. the cleanest fix would be to pass the logger explicitly as a parameter so every call-site controls its behaviour.
• If retaining the global instance is required (to avoid large surface changes) we could expose a top-level SetLogger that simply wraps slog.SetDefault, preserving today's pattern while still allowing replacement.

Please let me know if this would be of interest and, if so, what your thoughts on the implementation would be.