FQM-280: Verify coverage information system actions only add/update the coverage-information extension

[tstrass]

Summary

This updates the CRD 2.2.1 server Coverage Information system action validation test to verify resp-37: when a server returns a Coverage Information update, the returned resource may only add or modify the coverage-information extension and must not change any other resource content. I was on the fence about putting it in this test or adding a new test. Happy to switch it to its own test if reviewers prefer.

To get a source resource to compare against, we pull from the hook request context, prefetch, or mock_ehr_bundle as needed across hook types. If we can't find one, we emit a warning.

Testing Guidance

• Run the server suite against the client suite using the presets.
• You should see no new errors or warnings for the coverage info system action validation test. There will be some existing errors and warnings for some hooks, unrelated to these changes.
• Note this demonstrates passing behavior for every hook except encounter-start, which doesn't return a coverage information systemAction.

Anticipated Provider-side Test Impact

None

[arscan]

FYI @karlnaden, thanks!