[magnusp]

Add the Protobuf encoding for Hrana 3 over WebSocket (hrana3-protobuf subprotocol, binary frames). JSON stays the default. A URL of jdbc:libsql:ws://host:port?encoding=protobuf selects it.

Fixes #188.

This PR is stacked on #190 and targets feat/i187-hrana-ws-json. Merge #190 first.

What changes

• HranaWsProtobufCodec implements HranaWsCodec over the already vendored hrana_ws.proto and hrana.proto schemas. It maps Stmt, Value, Batch, BatchCond, StmtResult, and BatchResult both ways.
• LibsqlClientConfig gains an Encoding enum (JSON, PROTOBUF) as its last component. The existing constructors still default to JSON.
• LibsqlUrlParser reads encoding=json|protobuf|proto. An unknown value throws, and encoding=protobuf on an http or https URL throws because Protobuf over HTTP is out of scope.
• LibsqlWebSocketClient derives the subprotocol from the codec, hrana3 for JSON and hrana3-protobuf for Protobuf, and rejects a server that negotiates a different one.
• LibsqlDriver selects the codec from the encoding.

No new dependency. protobuf-java and the codegen were already present.

Evidence

• ./mvnw -q -pl libsql-hrana-codec,libsql-client,libsql-jdbc -am test passes.
• ./mvnw -q spotless:check passes.
• DOCKER_CONFIG="$PWD/libsql-conformance/src/test/docker-config" ./mvnw -pl libsql-itests -am -Dit.test='WebSocket*TransportIT' -DfailIfNoTests=false verify passes 8 of 8, split as WebSocketTransportIT 5 of 5 on JSON and WebSocketProtobufTransportIT 3 of 3 on Protobuf.

The Protobuf integration test covers typed select values including Long.MIN_VALUE and a blob, transaction commit and rollback, and error mapping. The codec unit test covers Long.MIN_VALUE, Long.MAX_VALUE, doubles, unicode text, null, empty and non-empty blobs, named arguments, batch conditions, and both error messages.

Limits

• Protobuf over HTTP (v3-protobuf/pipeline) is out of scope.
• wss has no TLS integration test. The container runs plain ws.
• Cursor requests are not implemented. Nothing in the driver uses them.