feat(studio): Initial RPC infrastructure and subsystems.

* UART and BLE/GATT transports for a protobuf encoded RPC
  request/response protocol.
* Custom framing protocol is used to frame a give message.
* Requests/responses are divided into major "subsystems" which
  handle requests and create response messages.
* Notification support, including mapping local events to RPC
  notifications by a given subsystem.
* Meta responses for "no response" and "unlock needed".
* Initial basic lock state support in a new core section, and allow specifying
  if a given RPC callback requires unlocked state or not.
* Add behavior subsystem with full metadata support and examples of
  using callback to serialize a repeated field without extra stack space needed.

Co-authored-by: Cem Aksoylar <caksoylar@users.noreply.github.com>

app/west.yml

@@ -29,5 +29,13 @@ manifest:
           - openthread
           - edtt
           - trusted-firmware-m
+    - name: nanopb
+      revision: 65cbefb4695bc7af1cb733ced99618afb3586b20
+      path: modules/lib/nanopb
+      remote: zephyrproject-rtos
+    - name: zmk-studio-messages
+      revision: 42446798e357e8021c5202a01ea250a34a776e85
+      path: modules/msgs/zmk-studio-messages
+      remote: zmkfirmware
   self:
     west-commands: scripts/west-commands.yml