Add resource measurement for “tasks”

[mdekstrand]

This adds a task concept to logging, so that we can measure resource usage.

[codecov]

Codecov Report

Attention: Patch coverage is 87.85047% with 26 lines in your changes missing coverage. Please review.

Project coverage is 90.30%. Comparing base (19f03d5) to head (a3bd64d).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
lenskit/lenskit/logging/tasks.py	84.92%	19 Missing ⚠️
lenskit/lenskit/logging/resource.py	92.00%	4 Missing ⚠️
lenskit/lenskit/logging/monitor.py	83.33%	2 Missing ⚠️
lenskit/lenskit/logging/worker.py	90.90%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #548      +/-   ##
==========================================
+ Coverage   90.23%   90.30%   +0.06%     
==========================================
  Files          98      100       +2     
  Lines        5756     5950     +194     
==========================================
+ Hits         5194     5373     +179     
- Misses        562      577      +15     

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