[RunInference] Reject use_model_manager with a multi-model KeyedModelHandler

[schizophrenicmaniac]

When a KeyedModelHandler is built from a list of KeyModelMappings, load_model() returns a _ModelHandlerManager. That object then loads and caches the per-key models itself, using its own count-based LRU. With use_model_manager=True, ModelManager only sees that wrapper, so the real models skip its memory tracking and eviction, and KeyModelPathMapping side-input updates don't work either.

This PR takes the validation route from the issue. RunInference now raises a ValueError at construction time when use_model_manager=True is used with a multi-model KeyedModelHandler, including when it's wrapped by with_preprocess_fn, with_postprocess_fn or with_no_batching. The error suggests max_models_per_worker_hint instead. Single-model KeyedModelHandlers are unaffected. I also documented use_model_manager and model_manager_args in the RunInference docstring and added a note to KeyedModelHandler.

Added a test in base_test.py that covers the plain and wrapped cases, plus the combinations that should still be allowed.

Fixes #40539

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.93%. Comparing base (76f6e6d) to head (25cc5e9).
⚠️ Report is 162 commits behind head on master.

Additional details and impacted files

@@              Coverage Diff              @@
##             master   #40574       +/-   ##
=============================================
+ Coverage     56.16%   79.93%   +23.76%     
=============================================
  Files          1124      488      -636     
  Lines        178336    82353    -95983     
  Branches       1489        0     -1489     
=============================================
- Hits         100170    65829    -34341     
+ Misses        75645    16524    -59121     
+ Partials       2521        0     -2521     

Flag	Coverage Δ
go	?
java	?
python	79.93% <100.00%> (+0.37%)	⬆️

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[github-actions]

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[jrmccluskey]

Looping in Valentyn who has more context on this bug

[tvalentyn]

R: @AMOOOMA mind taking a look? Thanks!

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[AMOOOMA]

LGTM, thanks!

[tvalentyn]

@schizophrenicmaniac could you resolve the conflicts please? thanks!