CBG-5144 add test for existing DCP checkpoint prefixes

[torcolvin]

CBG-5144 add test for existing DCP checkpoint prefixes

Add a test to make sure any DCP refactoring doesn't break checkpoint names.

Integration Tests

• GSI=true,xattrs=true https://jenkins.sgwdev.com/job/SyncGatewayIntegration/247/

[Copilot]

Pull request overview

This PR adds tests to ensure DCP checkpoint prefixes remain stable across refactoring efforts. The tests verify that checkpoint naming conventions for resync and attachment migration operations don't break unexpectedly.

Changes:

• Added comprehensive test coverage for DCP checkpoint prefix formats across different collection and metadata ID scenarios
• Updated attachment compaction functions to return checkpoint prefixes for verification
• Enhanced existing tests to validate checkpoint prefix values

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
db/background_mgr_resync_dcp_test.go	Added test verifying resync DCP checkpoint prefix format across various collection/groupID combinations
db/background_mgr_attachment_migration_test.go	Added test verifying attachment migration DCP checkpoint prefix format and removed obsolete comment
db/background_mgr_attachment_compaction.go	Updated to consume additional return value from sweep phase function
db/attachment_compaction_test.go	Enhanced tests to capture and validate checkpoint prefixes from compaction phases
db/attachment_compaction.go	Modified sweep and cleanup phase functions to return checkpoint prefixes for testing

[Copilot]

Remove extra whitespace between 'with' and 'an' - there is a tab character instead of a single space.

Suggested change

	// attachmentCompactCleanupPhase runs a DCP feed to clean up all documents with an attachment compaction xattr. Returns
	// attachmentCompactCleanupPhase runs a DCP feed to clean up all documents with an attachment compaction xattr. Returns