fix: add coverage pragmas for _NoCloseTextIOWrapper methods

Both close() and __del__ are no-op overrides that prevent TextIOWrapper
from closing real stdio handles. They are not directly tested in this PR
(the test is on #2821) and __del__ relies on GC timing which is
unreliable in tests.

Author: Nova

src/mcp/server/stdio.py

@@ -38,12 +38,12 @@ class _NoCloseTextIOWrapper(TextIOWrapper):
     print() or input() calls in the parent process.
     """
 
-    def close(self) -> None:
+    def close(self) -> None:  # pragma: lax no cover
         # Intentionally not closing the underlying buffer.
         # The standard process handles should outlive the server.
         pass
 
-    def __del__(self) -> None:
+    def __del__(self) -> None:  # pragma: lax no cover
         # Prevent TextIOWrapper.__del__ from calling close().
         pass