[Bulk transition] PR-1881: Conflict handling & automatic per-subset retry

[stevetrinh]

This pull request adds configurable retry and failure handling options to bulk state transitions in Statesman, making ActiveRecord adapter behavior more robust and flexible in the face of persistent insert conflicts. The main changes introduce new on_failure and conflict_retry_attempts options, allow callers to control how many times a bulk insert is retried after a conflict, and determine whether to raise or collect failures after retries are exhausted. These options are threaded through all relevant code paths and validated for correctness. Comprehensive tests are added to ensure the new behaviors work as intended.

Bulk transition retry and failure handling improvements:

• Added on_failure: and conflict_retry_attempts: options to BulkTransition.call and bulk_create methods, allowing callers to specify how many times to retry bulk inserts after a conflict and whether to raise or collect failures when retries are exhausted. [1] [2] [3] [4] [5]
• Updated the BulkCreate logic to respect the new options: after exhausting retries, it either raises a new BulkTransitionConflictError (wrapping the original RecordNotUnique) or collects all conflicted items as failures, depending on on_failure.

API and interface consistency:

• Ensured the in-memory adapter (Adapters::Memory) accepts the new options for interface parity, even though they have no effect in that context.
• Threaded the new options through all call paths and constructors, updating method signatures and internal state accordingly. [1] [2] [3]

Validation and error handling:

• Added validation to ensure conflict_retry_attempts is a positive integer, raising an ArgumentError otherwise.

Testing improvements:

• Added and updated tests to cover the new options, including scenarios for persistent conflicts, custom retry counts, and both :collect and :raise failure modes. [1] [2] [3]