fix: prevent cross-process stale writes to maxRevision.json

[WillieRuemmele]

Summary

• Before writing maxRevision.json, merge in-memory state with the current on-disk state
• For each member present in both, take the higher lastRetrievedFromServer (never regress)
• Also take the max serverMaxRevisionCounter

This prevents a long-lived process (e.g. VS Code Salesforce Extension) from overwriting correctly-synced values with its stale in-memory cache. The extension holds a cached RemoteSourceTrackingService singleton that was initialized on workspace open — when its background source-tracking check triggers a write, it would dump stale data back to disk, clobbering the CLI's correct writes.

Fixes forcedotcom/cli#3612

Test plan

• Existing unit tests pass (111/111)
• New unit tests cover: stale process can't regress values, null/undefined can't overwrite valid numbers, serverMaxRevisionCounter takes the max
• Manual validation: open VS Code with SF extension, run sf project reset tracking + sf project deploy start from external terminal, confirm lastRetrievedFromServer is no longer nullified