Test custom slot supplier metadata fields

[yafi-s]

The existing custom slot supplier test checks which slot kinds are observed but does not check the metadata fields, and never executes a local activity. Extend it to validate workflow names and sticky flags, activity names, and Nexus service/operation names when slots are marked used and released.

Record the reservation kind on each permit to distinguish the structurally identical activity protocols. Check captured metadata outside the supplier callbacks, where assertion failures cannot be swallowed by the SDK's callback wrapper.

Fixes #1079.

Validation:

• Four slot-supplier tests passed against the local dev server on Windows / Python 3.12, using the 1.32.0 wheel's native bridge with this checkout's Python source.
• An intentionally wrong expected workflow name made the modified test fail at the expected assertion; the mutation was reverted.
• Ruff imports/format, Pyright, basedpyright, and mypy passed for the changed file; git diff --check passed.
• Full poe lint was attempted but stopped at type checking in the minimal environment, which lacks optional integration dependencies. Full CI remains pending.

AI-assisted contribution, opened as a draft for contributor review before requesting maintainer review.

[CLAassistant]

All committers have signed the CLA.