[ibain]

This follows #228, where you suggested two pieces and new .proto files. I'm new to this repo, so please tell me if anything should be done differently. I'm happy to change it, or to split it up.

Why
The Android app (3.17.0) locks and unlocks with a signed sendParallaxPayload and reports progress on vehicleCommandStatePx. The client can do neither yet.

What

• Rivian.send_parallax_command sends a signed command, and Rivian.subscribe_for_parallax_command_state follows it.
• rivian.parallax gets encode_command, decode_command_state_message, encode_lock / encode_unlock and LOCK_RVM / UNLOCK_RVM.
• A new command.proto, and lock/unlock messages in body.proto, with regenerated modules.
• A short README example.

Testing

• ruff, mypy and pytest pass (280 tests).
• A golden test pins the bytes of an unlock that a real vehicle carried out (the ids are made up and the signature is injected), and the signature is checked against an independent HMAC.
• I tried it on an R1T with app 3.17.0, from Home Assistant: unlock (including from sleep, where Rivian woke the vehicle) and lock.
• I haven't tried a bad signature, closure commands, or how long a signed payload stays valid.

Things I wasn't sure about

• The signature reuses generate_ble_command_hmac, since it is a raw HMAC of some bytes. I can add a separate helper if that reads better.
• I moved the debug logging in core.py into _debug_message so the new decoder doesn't copy it. I can put it back and duplicate it if you'd rather not touch core.py.
• The app only sends body commands this way to vehicles that list PVS_BD_CMD. I don't know how other vehicles respond, so the docs say so.
• The keys are keyword-only, because three strings in a row are easy to swap when the command unlocks a vehicle.

It is four commits, to read in order: the schema and generated modules; core.py with command.py; the two Rivian methods; the README. If it is easier to review in two parts (codec first, then the methods), I'm glad to split it.