CBG-4413: Add logging capture to Sync Function diagnostic API

[bbrks]

CBG-4413

Captures log output from sync function execution to be piped back into the diagnostic API response

• Also fixes regression in SyncRunner pool use from Diagnostic API
• Refactor tests for clearer test cases and improved reliability

Example:

function(doc){
	console.log("this is my doc: "+JSON.stringify(doc));
	console.error("oops!");
	channel(doc.channels);
}

$ curl http://localhost:4987/db1/_sync -H 'Content-Type: application/json' -d '{"doc":{"foo":"bar","channels":["asdf"]}}' | jq
{
  "channels": [
    "asdf"
  ],
  "access": {},
  "roles": {},
  "logging": {
    "errors": [
      "oops!"
    ],
    "info": [
      "this is my doc: {\"_id\":\"\",\"_rev\":\"1-4f209ea9d3dd051b91697a7d5dbf78a6\",\"channels\":[\"asdf\"],\"foo\":\"bar\"}"
    ]
  }
}

Integration Tests

• GSI=true,xattrs=true https://jenkins.sgwdev.com/job/SyncGatewayIntegration/209/

[Copilot]

Pull request overview

This PR adds logging capture functionality to the Sync Function diagnostic API, allowing console.log and console.error output from sync function execution to be returned in the API response. The changes also fix a regression related to SyncRunner pool usage and refactor tests for improved clarity and reliability.

Key changes:

• Added logging capture via callback functions to sync function dry runs
• Refactored sync function dry run tests for better test case organization
• Fixed SyncRunner instantiation to create new instances for dry runs instead of using the database's pooled runner

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 1 comment.

File	Description
rest/diagnostic_doc_api.go	Added logging capture fields and callback functions to collect console output during sync function execution
rest/diagnostic_doc_api_test.go	Refactored test cases to use clearer naming and structure, added tests for logging capture functionality
db/crud.go	Modified SyncFnDryrun to create dedicated sync runner instances with logging callbacks instead of reusing database's channel mapper
channels/sync_runner.go	Added NewSyncRunnerWithLogging function to support custom logging callbacks and refactored NewSyncRunner to use it

[Copilot]

The comment on line 1363 is duplicated from line 1362. The comment should clarify that line 1364 tests for a forbidden field in the document body, not an invalid type.

Suggested change

	// invalid doc body type
	// forbidden field in doc body

[RIT3shSapata]

LGTM