[#37198] Make withBackOffSupplier public to enable bounded retry configuration

[PDGGK]

What changes are being proposed in this pull request?

This PR addresses issue #37198 by making the withBackOffSupplier() method public in RequestResponseIO, allowing users to configure bounded backoff to prevent infinite retry loops.

Problem

Users cannot configure bounded retries because the withBackOffSupplier() method has package-private visibility. This leads to:

• Inability to set retry limits (e.g., FluentBackoff.DEFAULT.withMaxRetries(3))
• Risk of infinite retry loops in production
• No way to control retry behavior for different failure scenarios

Solution

Changed withBackOffSupplier() visibility from package-private to public:

// Before:
RequestResponseIO<RequestT, ResponseT> withBackOffSupplier(SerializableSupplier<BackOff> value)

// After:
public RequestResponseIO<RequestT, ResponseT> withBackOffSupplier(
    SerializableSupplier<BackOff> value)

This allows users to configure bounded retries:

RequestResponseIO.of(caller, coder)
  .withBackOffSupplier(() -> FluentBackoff.DEFAULT.withMaxRetries(3).backoff())

Testing

Added comprehensive integration test givenBoundedBackoff_thenRetriesStopAfterLimit() that:

• Uses a serializable BoundedBackOff class with zero delays (no real sleeps)
• Verifies with PAssert that responses are empty and exactly 1 failure is emitted
• Verifies with metrics that call count = maxRetries + 1 (initial call + 3 retries)
• Verifies with metrics that failure count = 1

Test results:

• ✅ ./gradlew :sdks:java:io:rrio:check passes
• ✅ All existing tests continue to pass
• ✅ New test validates bounded retry behavior

Impact

• User benefit: Users can now prevent infinite retry loops by configuring bounded backoff
• Backward compatibility: No breaking changes; existing code continues to work
• Production readiness: Enables safer retry configurations for production workloads

Fixes #37198
Related to #37176

[gemini-code-assist]

Summary of Changes

Hello @PDGGK, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical limitation in RequestResponseIO by making the withBackOffSupplier() method publicly accessible. This modification enables users to implement bounded retry mechanisms, effectively preventing potential infinite retry loops in production environments and offering enhanced control over error handling. The update ensures safer and more predictable retry configurations without introducing any breaking changes to existing functionality.

Highlights

• Method Visibility Change: The withBackOffSupplier() method in RequestResponseIO has been changed from package-private to public, allowing external configuration of backoff strategies.
• Bounded Retry Configuration Enabled: This change empowers users to configure bounded retries, preventing infinite retry loops and providing granular control over retry behavior for various failure scenarios.
• New Integration Test: A comprehensive integration test, givenBoundedBackoff_thenRetriesStopAfterLimit(), was added to validate the new bounded retry functionality, including verification of call and failure counts using metrics.

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[github-actions]

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R: @Abacn for label java.

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[damccorm]

Thanks!