dataconnect(feat): add "jitter" to exponential backoff logic when reconnecting realtime streaming connections

[dconeybe]

This PR integrates random jitter into the exponential backoff strategy used by firebase-dataconnect when reconnecting query subscriptions. This is achieved by wiring a Random instance from FirebaseDataConnectRegistrar through to DataConnectBidiConnectStream to introduce random jitter between -0.5 and 0.5 to the exponential backoff calculation. This helps reduce thundering herd problems on reconnects.

Highlights

• Jittered Exponential Backoff: Configured DataConnectBidiConnectStream to use a random jitter factor (varying between -0.5 and 0.5) with RetryBackoffCalculator for reconnecting query subscriptions.
• Random Source Wiring: Threaded a Random instance from FirebaseDataConnectRegistrar down through FirebaseDataConnectFactory, FirebaseDataConnectImpl, and DataConnectGrpcRPCs to DataConnectBidiConnectStream.
• Improved Test Coverage: Expanded the subscription retry tests in QuerySubscriptionImplUnitTest to cover zero, minimum, maximum, and varying jitter using property-based tests.
• Test Code Consolidation: Created RetryBackoffCalculatorTesting to share common backoff test constants and generators, reducing duplication across test files.

Changelog

• CHANGELOG.md
  • Updated to document the jitter addition under the current release section.
• DataConnectBidiConnectStream.kt
  • Added a Random parameter to the constructor and initialized RetryBackoffCalculator with a lambda generating jitter between -0.5 and 0.5.
• DataConnectGrpcRPCs.kt
  • Added random: Random constructor parameter and passed it when instantiating DataConnectBidiConnectStream.
• FirebaseDataConnectFactory.kt
  • Added random: Random constructor parameter, used it to initialize idStringGenerator, and passed it to FirebaseDataConnectImpl.
• FirebaseDataConnectImpl.kt
  • Added random: Random constructor parameter and passed it to DataConnectGrpcRPCs.
• FirebaseDataConnectRegistrar.kt
  • Configured dependency injection to pass Random.Default to FirebaseDataConnectFactory.
• RetryBackoffCalculator.kt
  • Removed default argument for getRandomJitter constructor parameter to require caller-specified jitter strategy.
• DataConnectGrpcRPCsUnitTest.kt
  • Updated constructor call to pass Random.Default.
• FirebaseDataConnectImplUnitTest.kt
  • Updated constructor call to pass Random.Default.
• QuerySubscriptionImplUnitTest.kt
  • Updated test helper to accept Random and verify that connection retry wait times match expected exponential backoff with zero, min, max, or varying jitter.
• RetryBackoffCalculatorTesting.kt
  • Created a new test utility object to hold shared constants (backoffValues, minJitterBackoffValues, maxJitterBackoffValues) and an Arb generator for jitter test cases.
• RetryBackoffCalculatorUnitTest.kt
  • Refactored to use the shared constants in RetryBackoffCalculatorTesting and updated calculator instantiation to provide explicit jitter lambdas.

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[dconeybe]

/gemini review

[gemini-code-assist]

Code Review

This pull request refactors the backoff calculation mechanism in Firebase Data Connect to support customizable random jitter. The RetryBackoffCalculator now requires a jitter generator function, and a Random instance is passed down from the registrar through the factory, implementation, and gRPC classes to the stream. Unit tests have been updated and expanded with a new helper file RetryBackoffCalculatorTesting.kt to verify exponential backoff behavior under various jitter conditions. No review comments were provided, so there is no additional feedback.

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