Add signed Parallax lock/unlock commands #228

I'd like to add the Parallax way of locking and unlocking to the client, and want to agree on the shape before opening a PR.

What the app does. Android app 3.17.0 sends lock/unlock as sendParallaxPayload (SendRemoteCommand) with a signed protobuf: an HMAC-SHA256 over a serialized operation (body.locks.unlock / body.locks.lock), keyed with the same phone-key secret send_vehicle_command already derives. It then follows a vehicleCommandStatePx subscription for the result. There is no separate WAKE_VEHICLE: the request itself wakes a sleeping vehicle. The vehicle needs PVS_BD_CMD in supportedFeatures.

Tested. On an R1T with an enrolled phone key: unlock on a sleeping vehicle (waking, executing, success in 26 s) and lock on an awake one. The message layouts are written up in kaedenbrinkman/rivian-api (app/parallax/commands/body-commands.md).

Why here. I have this working in the Home Assistant integration, but it has to reach into _start_subscription and __graphql_query. Public methods would remove that.

Proposal. .proto files for the envelope, operation and state messages (like operation.proto), an encoder and decoder in rivian.parallax, and on Rivian a method to send a signed body command and one to follow its state.

Questions

1. One call that sends and waits for completion, or the two pieces (send, subscribe) with a small helper on top? I lean to the pieces.
2. Fine to add the new .proto files and generated modules?
3. Add keyless vehicle operations for Gen 2 #218 added keyless send_vehicle_operation. This is a different, signed mutation, so I don't think they overlap. Say so if you see it differently.
4. Is anyone already working on this?

Not tested: a bad or missing signature, closure commands (frunk, windows), failure paths. I'll open the integration PR once there is a client release.