Go BSON encoders/decoders currently use a "registry" to look up codecs for specific Go types, which uses a sync.Map to find the correct codec. However, that creates possible locking contention between goroutines, requires reflection calls, and uses a relatively slow map lookup compared to a simple type switch. The sync.Map lookup is only necessary when a customer overrides the default registry, which few customers do. Instead, it would be better to use a type switch for common Go types, only falling back to a sync.Map for custom registries or user-defined types.

See ReflectionFreeDCodec type that was originally developed to significantly improve BSON encode/decode performance, specifically for the bson.D type.

Definition of done:

• Use a type switch to look up BSON codecs for common Go types when the user has not provided a custom registry.