fix: make pywin32 imports soft to support server-only Windows installs

Wrap pywin32 imports in try/except ImportError so that server-only
Windows users are not forced to install pywin32. The package is only
needed for Job Object support in mcp.client.stdio, but the eager
import in mcp/__init__.py pulls it in for all users.

All downstream functions (_create_job_object, _maybe_assign_process_to_job,
terminate_windows_process_tree) already null-check these modules before
use, so graceful degradation is fully covered.

Fixes server-only deployments that fail with pywin32 installation errors
when antivirus software locks extracted DLLs during uv cache cleanup.

Github-Issue: #2233
Reported-by: Nikhil Suresh

Author: herakles-dev

src/mcp/os/win32/utilities.py

@@ -17,10 +17,18 @@
 
 # Windows-specific imports for Job Objects
 if sys.platform == "win32":
-    import pywintypes
-    import win32api
-    import win32con
-    import win32job
+    try:
+        import pywintypes
+        import win32api
+        import win32con
+        import win32job
+    except ImportError:
+        # pywin32 is not installed — degrade gracefully.
+        # All downstream code null-checks these modules before use.
+        pywintypes = None
+        win32api = None
+        win32con = None
+        win32job = None
 else:
     # Type stubs for non-Windows platforms
     win32api = None