core.cachew: make disabled_cachew defensive

my/core/cachew.py

@@ -20,7 +20,12 @@ def disable_cachew():
 
 @contextmanager
 def disabled_cachew():
-    import cachew
+    try:
+        import cachew
+    except ModuleNotFoundError:
+        # no need to disable anything
+        yield
+        return
     old = disable_cachew()
     try:
         yield

my/core/common.py

@@ -202,6 +202,7 @@ if TYPE_CHECKING:
 
     mcachew: McachewType
 
+# TODO ugh. I think it needs doublewrap, otherwise @mcachew without args doesn't work
 def mcachew(*args, **kwargs): # type: ignore[no-redef]
     """
     Stands for 'Maybe cachew'.