Improve logging in Ray cluster setups

[mdekstrand]

This adds several improvements and bug-fixes for subprocess logging when running in a Ray cluster.

[codecov]

Codecov Report

Attention: Patch coverage is 63.63636% with 12 lines in your changes missing coverage. Please review.

Project coverage is 90.96%. Comparing base (f877fd3) to head (2085049).
Report is 12 commits behind head on main.

Files with missing lines	Patch %	Lines
src/lenskit/parallel/ray.py	33.33%	10 Missing ⚠️
src/lenskit/logging/monitor.py	0.00%	1 Missing ⚠️
src/lenskit/logging/worker.py	90.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #673      +/-   ##
==========================================
- Coverage   91.03%   90.96%   -0.08%     
==========================================
  Files         132      132              
  Lines        9078     9096      +18     
==========================================
+ Hits         8264     8274      +10     
- Misses        814      822       +8     

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