feat: add MongoDB driver handshake metadata - #1937

Activates the pre-existing driver=DriverInfo(...) call in _connect_to_mongodb_atlas, so that MongoDB server-side telemetry (db.currentOp, Atlas dashboards, mongos/d logs) can identify traffic from DocArray applications.

On first connection, mongod emits a client metadata log entry. With this change the entry will look like:

{"t":{"$date":"2026-07-21T09:15:42.123+00:00"},"s":"I","c":"NETWORK","id":51800,"ctx":"conn1","msg":"client metadata","attr":{"remote":"192.168.1.10:54321","client":"conn1","negotiatedCompressors":[],"doc":{"driver":{"name":"PyMongo|DocArray","version":"4.9.2|0.41.0"},"os":{"type":"Darwin","name":"Darwin","architecture":"arm64","version":"26.5.2"},"platform":"CPython 3.10.3.final.0"}}}

The PyMongo|DocArray naming follows the MongoDB handshake specification for layered driver attribution.