Add ChildWorkflowOptions support to WorkflowImplementationOptions (#2)

[porunov]

Fixes #2790

Tests are added to: ChildWorkflowOptionsInWorkflowImplementationOptionsTest.java

• Add childWorkflowOptions map and defaultChildWorkflowOptions fields
• Add setChildWorkflowOptions() and setDefaultChildWorkflowOptions() builder methods
• Add getChildWorkflowOptions() and getDefaultChildWorkflowOptions() getters
• Update SyncWorkflowContext to store and expose child workflow options
• Update WorkflowInternal.newChildWorkflowStub() to merge predefined options
• Add mergeChildWorkflowOptions() method to ChildWorkflowOptions.Builder
• Add integration and unit tests

Potential documentation place: https://docs.temporal.io/develop/java/workflows/child-workflows (it could be something similar as activity options documentation).

Disclaimer: Code was Generated by Opus 4.6 in Copilot. Reviewed manually.

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[maciejdudko]

Hi @porunov, thank you for your contribution. The code looks good, but the tests need to be improved before we can merge this - see comment.

[maciejdudko]

This test does not actually assert that the right options were used. Please rewrite it so that the child workflow only succeeds if the default options were correctly applied. I think checking its memo would be most straight forward.

Please also add a test that verifies default, not per-type child workflow options work too.