feat: add support for configuring a debug logger

[dnaeon]

This PR adds support for configuring a debug logger for inspecting how the recorder adds/records/replays interactions.

The recorder.WithDebugWriter option allows API clients to specify their own io.Writer, which will be used to configure an slog.Logger for emitting debug-only events.

By default the Recorder and Cassette will be configured with io.Discard writer, so no debug logs will be emitted.

In order to enable debug logger for existing test cases without having to set the recorder.WithDebugLogger option API clients can set the VCR_DEBUG=true env var, which will configure a logger emitting events to os.Stderr.

Related to #108

cc: @marco-m , @akosyakov

[codecov-commenter]

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Codecov Report

❌ Patch coverage is 71.32616% with 80 lines in your changes missing coverage. Please review.
✅ Project coverage is 55.97%. Comparing base (fd3e9bc) to head (854bb3e).
⚠️ Report is 1 commits behind head on v4.

Files with missing lines	Patch %	Lines
pkg/cassette/cassette.go	46.00%	50 Missing and 4 partials ⚠️
pkg/recorder/recorder.go	87.42%	15 Missing and 7 partials ⚠️
pkg/recorder/middleware.go	0.00%	4 Missing ⚠️
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Additional details and impacted files

@@            Coverage Diff             @@
##               v4     #148      +/-   ##
==========================================
+ Coverage   50.96%   55.97%   +5.01%     
==========================================
  Files           5        5              
  Lines         520      720     +200     
==========================================
+ Hits          265      403     +138     
- Misses        235      293      +58     
- Partials       20       24       +4     

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[dnaeon]

@marco-m , a bunch of other places got debug events as well, please check them as well, thanks!

[marco-m]

Hello @dnaeon, I did a first pass. Is there anything specific you want another pair of eyes for ?

[dnaeon]

Hello @dnaeon, I did a first pass. Is there anything specific you want another pair of eyes for ?

Thanks a lot, @marco-m !

I guess the real question is whether this change is helpful for debugging as the original request in #108

Unfortunately I don't think we would be able to provide a nice diff-like feature because of the reasons I've described in #108

[marco-m]

I guess the real question is whether this change is helpful for debugging as the original request in #108

Unfortunately I don't think we would be able to provide a nice diff-like feature because of the reasons I've described in #108

Yes, your explanations in #108 were very clear and helped me understand the constraints.

From my point of view, this is already a great improvement. Thank you!

[marco-m]

Thank you, as usual it is a pleasure to interact with you @dnaeon :-)