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>

docs/docusaurus.config.js

@@ -12,6 +12,7 @@ module.exports = {
   organizationName: "zmkfirmware", // Usually your GitHub org/user name.
   projectName: "zmk", // Usually your repo name.
   plugins: [
+    "@docusaurus/theme-mermaid",
     path.resolve(__dirname, "src/docusaurus-tree-sitter-plugin"),
     path.resolve(__dirname, "src/hardware-metadata-collection-plugin"),
     path.resolve(__dirname, "src/hardware-metadata-static-plugin"),
@@ -164,6 +165,7 @@ module.exports = {
     ],
   ],
   markdown: {
+    mermaid: true,
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       comments: false,
       admonitions: false,