test: add AsyncClientClass regression coverage

[amirdeljouyi]

Motivation and Context

Hey 👋

I added two regression tests for AsyncClientClass around async client generation behavior.

The endpoint-discovery override path, custom utilities generation, and repeated scheduled-executor field generation were not directly covered by the existing test suite.

Modifications

• Added asyncClientEndpointDiscovery_whenRequiredEndpointDiscoveryAllowsEndpointOverride_generatesFallbackAndWarning.
• Added asyncClientClass_withUtilitiesInstanceTypeAndExistingScheduledExecutor_addsExpectedCode.

Testing

These tests check that required endpoint discovery generates the expected fallback and warning when endpoint overrides are allowed, that utilities use the configured instance type, and that repeated field generation does not duplicate the scheduled executor.

Impact on coverage:

• Covers the endpoint-discovery warning and fallback, plus utilities generation and scheduled executor field generation.
• This improves line coverage for AsyncClientClass by about 4% and branch coverage by about 10%.

All 16 AsyncClientClassTest tests pass locally, and the targeted 46-module reactor package build succeeds.

Screenshots (if appropriate)

Not applicable.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)

Checklist

• I have read the CONTRIBUTING document
• Local run of mvn install succeeds
• My code follows the code style of this project
• My change requires a change to the Javadoc documentation
• I have updated the Javadoc documentation accordingly
• I have added tests to cover my changes
• All new and existing targeted tests passed
• I have added a changelog entry. Adding a new entry must be accomplished by running the scripts/new-change script and following the instructions. Commit the new file created by the script in .changes/next-release with your changes.
• My change is to implement 1.11 parity feature and I have updated LaunchChangelog

License

• I confirm that this pull request can be released under the Apache 2 license

I hope you find these tests useful. Please let me know if you have any questions or concerns.

Thanks,