feat(hot-runner): implement hot runner protocol with registry, health monitoring, and job dispatch (#791)

Adds persistent Unity editor instance support to reduce build iteration time
by eliminating cold-start overhead. Includes:

- HotRunnerTypes: interfaces for config, status, job request/result, transport
- HotRunnerRegistry: in-memory runner management with file-based persistence
- HotRunnerHealthMonitor: periodic health checks, idle recycling, job-count recycling
- HotRunnerDispatcher: job routing with wait-for-runner, timeout, and output streaming
- HotRunnerService: high-level API integrating registry, health, and dispatch
- 34 unit tests covering registration, filtering, health, dispatch, timeout, fallback
- action.yml inputs for hot runner configuration (7 new inputs)
- Input/BuildParameters integration for hot runner settings
- index.ts wiring with cold-build fallback when hot runner unavailable

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/model/build-parameters.ts

@@ -106,6 +106,13 @@ class BuildParameters {
   public cacheUnityInstallationOnMac!: boolean;
   public unityHubVersionOnMac!: string;
   public dockerWorkspacePath!: string;
+  public hotRunnerEnabled!: boolean;
+  public hotRunnerTransport!: 'websocket' | 'grpc' | 'named-pipe';
+  public hotRunnerHost!: string;
+  public hotRunnerPort!: number;
+  public hotRunnerHealthInterval!: number;
+  public hotRunnerMaxIdle!: number;
+  public hotRunnerFallbackToCold!: boolean;
 
   public static shouldUseRetainedWorkspaceMode(buildParameters: BuildParameters) {
     return buildParameters.maxRetainedWorkspaces > 0 && Orchestrator.lockedWorkspace !== ``;
@@ -242,6 +249,13 @@ class BuildParameters {
       cacheUnityInstallationOnMac: Input.cacheUnityInstallationOnMac,
       unityHubVersionOnMac: Input.unityHubVersionOnMac,
       dockerWorkspacePath: Input.dockerWorkspacePath,
+      hotRunnerEnabled: Input.hotRunnerEnabled,
+      hotRunnerTransport: Input.hotRunnerTransport,
+      hotRunnerHost: Input.hotRunnerHost,
+      hotRunnerPort: Input.hotRunnerPort,
+      hotRunnerHealthInterval: Input.hotRunnerHealthInterval,
+      hotRunnerMaxIdle: Input.hotRunnerMaxIdle,
+      hotRunnerFallbackToCold: Input.hotRunnerFallbackToCold,
     };
   }