feat: use sync.Map instead of custom lock

[crenshaw-dev]

keyLock just happens to fit one of the two recommended use cases for sync.Map: one where the map only grows.

I understand this trades memory for less lock contention. I expect our current use cases will see virtually no difference.

[sonarqubecloud[bot]]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[crenshaw-dev]

Gonna close this for now, because I haven't analyzed the different projects' different uses of this package. It's possible some of the use cases aren't appropriate for a sync map. Can revisit later.