Remove manylog and integrate a monitoring thread for worker logs

[mdekstrand]

This removes manylog and directly implements Structlog-compatible worker log aggregation in a monitoring thread in LensKit.

[codecov]

Codecov Report

Attention: Patch coverage is 71.07692% with 94 lines in your changes missing coverage. Please review.

Project coverage is 90.41%. Comparing base (11ef984) to head (c29c171).
Report is 19 commits behind head on main.

Files with missing lines	Patch %	Lines
lenskit/lenskit/logging/monitor.py	74.12%	37 Missing ⚠️
lenskit/lenskit/logging/worker.py	79.79%	20 Missing ⚠️
lenskit/lenskit/logging/progress/_rich.py	21.05%	15 Missing ⚠️
lenskit/lenskit/logging/_console.py	52.63%	9 Missing ⚠️
lenskit/lenskit/logging/config.py	40.00%	9 Missing ⚠️
lenskit/lenskit/logging/processors.py	0.00%	3 Missing ⚠️
lenskit/lenskit/parallel/worker.py	87.50%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #539      +/-   ##
==========================================
- Coverage   91.17%   90.41%   -0.77%     
==========================================
  Files          96       98       +2     
  Lines        5442     5720     +278     
==========================================
+ Hits         4962     5172     +210     
- Misses        480      548      +68     

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