[glrs]

This PR improves the operations consumer by ensuring only changed snapshots are written, reducing unnecessary writes and traffic to the DB. It also updates documentation and adds comprehensive tests to verify the new behavior.

Efficiency improvements to snapshot writing:

• The FileSpoolConsumer now writes a plan's snapshot only if its content (excluding updated_at) has changed since the last write by that consumer, or if the consumer has not written it before. This prevents redundant writes when no new events have occurred. [1] [2] [3]
• A new internal method _content_fingerprint computes a SHA-256 digest of a snapshot's content (excluding updated_at) to efficiently detect changes.

Documentation updates:

• The operational snapshots section in plan_execution.md is updated to clarify that only changed snapshots are written, and to describe the behavior when snapshots are deleted or when a consumer restarts.
• The docstring for OpsConsumerService is revised to reflect the new behavior of writing only changed snapshots.
• The docstring for FileSpoolConsumer is updated to describe the new snapshot writing logic.

Testing enhancements:

• A new test class, TestConsumerSkipsUnchangedSnapshots, is added to verify that unchanged snapshots are not rewritten, that new events trigger writes, that failed writes are retried, and that consumers write all snapshots on startup. CouchDB revision behavior is also tested.
• Supporting imports and setup code for these tests are included. [1] [2]

(References: [1] [2] [3] [4] [5] [6] [7] [8] [9]