Fix unchecked call warnings in SourceTest.java (#2625)

[AyushMhaisane]

This PR fixes compiler warnings related to "unchecked call to expectNext(I)" in SourceTest.java.

The issue was caused by TestSink.create(system) returning a raw type when not explicitly typed. This change adds the necessary type witnesses (e.g., , ) to the TestSink.create calls to ensure type safety and eliminate the warnings.

Changes

Updated SourceTest.java to use explicit types in TestSink.create (e.g., TestSink.<Integer>create(system)).

Updated Source creation where necessary to match the Sink types (e.g., Source.<String>fromArray(...)).

Related Issue Fixes #2625

Verification

Ran Test/compile in stream-tests module: Success (Warnings related to SourceTest.java are gone).

Ran testOnly org.apache.pekko.stream.javadsl.SourceTest: All tests passed.

Checklist:

[x] The commit message follows the [contribution guidelines](https://github.com/apache/pekko/blob/main/CONTRIBUTING.md).

[x] Tests have been run and passed.

[x] No logic changes, only type safety improvements.

[pjfanning]

there are now no changes in the PR - everything including the code fixes have been removed

[pjfanning]

Now all the unnecessary format changes are back.

[pjfanning]

the changes look good now but the import changes seem unnecessary

[AyushMhaisane]

Thanks @pjfanning. I have removed the unnecessary java.util.function.Function import and updated the commit. The diff should be cleaner now.

[pjfanning]

This is wrong too

[He-Pin]

@AyushMhaisane Thanks, the original problem is a type inference problem, so the fix should add some type parameter to the expectNext method in the testkit.

[pjfanning]

This doesn't compile and doesn't fix the compile warnings anyway.
This original issue is only a slight irritant so it might not be worth spending more time on it.