refactor: accept enum types in registry/manager signatures, remove 429 redundant...

refactor: accept enum types in registry/manager signatures, remove 429 redundant as-string casts

Widen buildRegistryKey, buildCaseInsensitiveCompositeKey, and
VariableMetadata.component to accept OCPP20ComponentName and VariableName
enums directly, eliminating 429 as-string casts across the registry and
variable manager. 8 casts retained on enum comparison lines required by
no-unsafe-enum-comparison lint rule.