Fix UnsupportedOperationException when merging ActivityOptions with i…

[nitishagar]

What was changed

Modified ActivityOptions.Builder.mergeActivityOptions() to create a new ArrayList when combining context propagators instead of calling addAll() directly on the existing list. Added a test to verify the fix.

Files changed:

• temporal-sdk/src/main/java/io/temporal/activity/ActivityOptions.java
• temporal-sdk/src/test/java/io/temporal/activity/ActivityOptionsTest.java

Why?

When users set context propagators using immutable lists (e.g., List.of() or Collections.emptyList()), merging ActivityOptions would throw UnsupportedOperationException because the code attempted to call addAll() on an immutable list.

This fix follows the approach suggested by @cretz in the issue: create a new list that combines both instead of modifying one of them.

Checklist

1. Closes Merging ActivityOptions fails with UnsupportedOperationException when using immutable lists for context propagators #2482

2. How was this tested:

   • Added unit test testActivityOptionsMergeWithImmutableContextPropagators that creates two ActivityOptions with immutable context propagator lists (Collections.emptyList()) and verifies they can be merged without throwing UnsupportedOperationException
   • All existing ActivityOptionsTest tests pass
   • Full build passes (./gradlew clean build)

3. Any docs updates needed?

   • No documentation updates needed - this is a bug fix with no API changes

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