fix(coding-agent): addressed python cleanup review findings

fixed retained-kernel restart and owner cleanup edge cases during recovery and disposal

tracked async user_python hooks during disposal-sensitive execution paths and hardened startup warmup tracking

strengthened cleanup and kernel lifecycle regressions to remove deadlocks, false positives, and timing flakes

packages/coding-agent/test/core/python-executor-session.test.ts

@@ -25,7 +25,7 @@ class FakeKernel {
 		return this.alive;
 	}
 
-	async shutdown(): Promise<{ confirmed: boolean }> {
+	async shutdown(): Promise<pythonKernel.KernelShutdownResult> {
 		this.shutdownCalls += 1;
 		this.alive = false;
 		return { confirmed: true };