Fix process status return type annotation

- Fix get_process_status return type: dict[str, Any] | None
- Function returns None when pid not found, or dict when found
- Corrects semantics from 'dict with nullable values' to 'optional dict'

Completes all critical typing issues from PR review comments

Author: Agent-Hellboy

mcp_fuzzer/fuzz_engine/runtime/manager.py

@@ -201,7 +201,7 @@ async def stop_all_processes(self, force: bool = False) -> None:
         tasks = [self.stop_process(pid, force=force) for pid in pids]
         await asyncio.gather(*tasks, return_exceptions=True)
 
-    async def get_process_status(self, pid: int) -> dict[str, Any | None]:
+    async def get_process_status(self, pid: int) -> dict[str, Any] | None:
         """Get status information for a specific process."""
         async with self._get_lock():
             if pid not in self._processes: