[Refactor][KVConnector]: Move KV Cache Events into KVConnectorWorkerMetadata

[hickeyma]

Purpose

This change removes kv_cache_events as a top-level field on KVConnectorOutput and instead carries KV cache events inside a connector-specific KVConnectorWorkerMetadata subclass (LMCacheWorkerMetadata). This aligns KV event transport with the generic worker-to-scheduler metadata mechanism introduced in PR #31964, eliminating redundant aggregation code paths.

This also resolves #28309 (review) to request support for KV events for multiple connectors.

Note: Do NOT merge until #31964 merges. Merged, good to go.

Test Plan

pytest -s -v tests/v1/kv_connector/unit/test_lmcache_connector.py

Test Result

Unit tests pass

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[gemini-code-assist]

Code Review

This pull request is a well-executed refactoring that moves KV cache event transport to a generic worker-to-scheduler metadata mechanism using KVConnectorWorkerMetadata. This change improves modularity and aligns the KV event transport with a more general pattern, which is a solid architectural improvement. The changes are consistently applied across the codebase, including base classes, LMCacheConnectorV1, MultiConnector, and the corresponding tests have been updated thoroughly. I have one suggestion to improve code clarity in MultiConnector.

[hickeyma]

Convert to draft for now as need to do more testing on it.

Ready for review.

[mergify]

This pull request has merge conflicts that must be resolved before it can be
merged. Please rebase the PR, @hickeyma.

https://docs.github.com/en/pull-requests/collaborating-with-pull-requests/working-with-forks/syncing-a-fork

[mergify]

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[mergify]

Hi @hickeyma, the pre-commit checks have failed. Please run:

uv pip install pre-commit
pre-commit install
pre-commit run --all-files

Then, commit the changes and push to your branch.

For future commits, pre-commit will run automatically on changed files before each commit.

Tip

Is mypy failing?

mypy is run differently in CI. If the failure is related to this check, please use the following command to run it locally:

# For mypy (substitute "3.10" with the failing version if needed)
pre-commit run --hook-stage manual mypy-3.10