Implement a proxy logger that suppresses debug & info messages by default

[mdekstrand]

This adds a custom get_logger function that returns a lazy logger that, when structlog has not been configured, uses a default logger that filters out debug and info messages.

All LensKit code should use this function instead of structlog.stdlib.get_logger or structlog.get_logger to get logger objects.

[codecov]

Codecov Report

Attention: Patch coverage is 97.43590% with 1 line in your changes missing coverage. Please review.

Project coverage is 90.71%. Comparing base (48eb645) to head (80fb41b).
Report is 8 commits behind head on main.

Files with missing lines	Patch %	Lines
lenskit/lenskit/logging/_proxy.py	92.30%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #583   +/-   ##
=======================================
  Coverage   90.70%   90.71%           
=======================================
  Files         105      106    +1     
  Lines        6512     6526   +14     
=======================================
+ Hits         5907     5920   +13     
- Misses        605      606    +1     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.