refactor: improve logging in src/proxy/processors, remove log-related stubs/spies in tests

[jescalada]

Fixes #1281, supersedes #1338

Also improves wording and log handling in general, and fixes log stubs in tests.

[netlify]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.01%. Comparing base (90df884) to head (bab1881).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1448      +/-   ##
==========================================
- Coverage   90.01%   90.01%   -0.01%     
==========================================
  Files          67       67              
  Lines        4769     4765       -4     
  Branches      885      884       -1     
==========================================
- Hits         4293     4289       -4     
  Misses        458      458              
  Partials       18       18              

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[jescalada]

@kriswest I reimplemented #1338 in case we want to get the rc5 out ASAP. Only this and the any/as PR (#1323) remain! 👍🏼