Guard np.dtype check in normalize_dtype for environments without numpy

When numpy is not available (e.g., WASM), the `np` name is undefined.
The has_numpy flag was already used elsewhere but this check was missed
when the numpy_stub was removed.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: kesmit13

singlestoredb/functions/signature.py

@@ -332,7 +332,7 @@ def normalize_dtype(dtype: Any) -> str:
     if isinstance(dtype, str):
         return sql_to_dtype(dtype)
 
-    if typing.get_origin(dtype) is np.dtype:
+    if has_numpy and typing.get_origin(dtype) is np.dtype:
         dtype = typing.get_args(dtype)[0]
 
     # Specific types