[serve] refactor _run_user_code

[zcin]

Why are these changes needed?

Refactor _run_user_code so that it returns an asyncio.future instead of concurrent.futures.Future.

This is exactly how we had it implemented originally. We changed _run_user_code to return a concurrent.futures.Future in order to support local testing mode because we need to access the concurrent.futures.Future for local testing mode (ref: #48449). However we can change it back and just add a condition for local testing mode.

This will be needed for supporting running user code on the same event loop.

[Copilot]

Pull Request Overview

Refactors internal user code invocation to use asyncio.Future by default and introduces local_testing_mode to preserve concurrent.Future behavior in local tests.

• Renamed and updated decorator to _run_user_code, removing asyncio.wrap_future usage around calls.
• Added local_testing_mode flag to UserCallableWrapper and propagated it in the local testing path.
• Removed redundant asyncio.wrap_future calls in various Replica methods.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
python/ray/serve/_private/replica.py	Replaced asyncio.wrap_future calls, updated decorator to _run_user_code, added local_testing_mode flag
python/ray/serve/_private/local_testing_mode.py	Passed local_testing_mode=True when creating the replica wrapper in local tests

Comments suppressed due to low confidence (3)

python/ray/serve/_private/replica.py:1220

• The new local_testing_mode parameter is required but has no default, yet not all instantiation sites were updated; consider providing a default of False or updating all UserCallableWrapper(...) calls to pass this flag.

        self._local_testing_mode = local_testing_mode

python/ray/serve/_private/replica.py:1250

• The docstring states the decorator always returns an asyncio.Future, but in local_testing_mode it returns a concurrent.futures.Future. Update the documentation to reflect this conditional behavior.

        """

python/ray/serve/_private/local_testing_mode.py:73

• Consider adding or updating tests to verify both branches of the local_testing_mode flag (True vs. False) to ensure the wrapper returns the expected Future type in each mode.

        local_testing_mode=True,

[zcin]

ping @akyang-anyscale @abrarsheikh for review, this one is pretty straightforward.