tools: Migrate to Protobuf RPC sessions

[str4d]

trafficstars

To-do:

• [x] Generate protobuf 0.20 bindings.
• RpcSession:
  • [x] Basic synchronous support.
  • [ ] Rewrite to be asynchronous and handle I/O in a separate task.
  • [ ] Protobuf version checking.
  • [ ] Handle command IDs correctly.
    • The session should be managing them, and not using 0 which is a broadcast ID.
  • [ ] Automatic session closing.

Working commands:

• [x] --bin storage -- mkdir
• [x] --bin storage -- remove
• [x] --bin storage -- size
• [x] --bin storage -- receive
• [ ] --bin storage -- send
• [x] --bin storage -- list
• [x] --bin storage -- md5sum
• [ ] --bin run-fap

Closes #76.

[str4d]

--bin storage -- list seems to be slower than the text CLI version. Not sure there's much we can do about that.

[str4d]

Rebased on main.

[str4d]

Force-pushed to clean up the protobuf generation and move the output files into a submodule, making room for other submodules under proto for organising the async impl.