Make bypassing capture context-aware

[alexhall]

This change makes the capture/bypass macro aware of the capture context in which it's running, so that it can more intelligently restore previous out/err writers (or just pass through if no capturing is active).

Unsupported corner cases:

• Nested capturing (will write to the next level up, not the original out/err)
• Code running on other threads where bindings weren't conveyed (will still write to the redef'ed out/err)

If this approach looks sensible, I'm happy to clean up the code, add tests, etc.

Fixes #446

[codecov]

Codecov Report

❌ Patch coverage is 85.71429% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 69.21%. Comparing base (15e553d) to head (1a7a7ad).
⚠️ Report is 24 commits behind head on main.

Files with missing lines	Patch %	Lines
src/kaocha/plugin/capture_output.cljc	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #447      +/-   ##
==========================================
+ Coverage   69.17%   69.21%   +0.04%     
==========================================
  Files          52       52              
  Lines        2819     2823       +4     
  Branches      187      187              
==========================================
+ Hits         1950     1954       +4     
  Misses        689      689              
  Partials      180      180              

Flag	Coverage Δ
unit	69.21% <85.71%> (+0.04%)	⬆️

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