TYP: misc fixes for numpy types
```
pandas/core/dtypes/cast.py:1491: error: Incompatible return value type (got "Type[object]", expected "Union[dtype, ExtensionDtype]")  [return-value]
pandas/core/dtypes/cast.py:1553: error: Incompatible types in assignment (expression has type "Type[object]", variable has type "Union[dtype, ExtensionDtype]")  [assignment]
pandas/core/construction.py:601: error: Incompatible default for argument "dtype_if_empty" (default has type "Type[object]", argument has type "Union[ExtensionDtype, str, dtype, Type[str], Type[float], Type[int], Type[complex], Type[bool]]")  [assignment]
pandas/core/generic.py:6217: error: Argument "dtype_if_empty" to "create_series_with_explicit_dtype" has incompatible type "Type[object]"; expected "Union[ExtensionDtype, str, dtype, Type[str], Type[float], Type[int], Type[complex], Type[bool]]"  [arg-type]
pandas/tests/arrays/sparse/test_dtype.py:97: error: Argument 1 to "SparseDtype" has incompatible type "Type[object]"; expected "Union[ExtensionDtype, str, dtype, Type[str], Type[float], Type[int], Type[complex], Type[bool]]"  [arg-type]
pandas/tests/arrays/sparse/test_dtype.py:172: error: Argument 1 to "SparseDtype" has incompatible type "Type[object]"; expected "Union[ExtensionDtype, str, dtype, Type[str], Type[float], Type[int], Type[complex], Type[bool]]"  [arg-type]
pandas/tests/arrays/sparse/test_combine_concat.py:44: error: Argument 1 to "SparseDtype" has incompatible type "Type[object]"; expected "Union[ExtensionDtype, str, dtype, Type[str], Type[float], Type[int], Type[complex], Type[bool]]"  [arg-type]
pandas/tests/arrays/sparse/test_array.py:561: error: Argument 1 to "SparseDtype" has incompatible type "Type[object]"; expected "Union[ExtensionDtype, str, dtype, Type[str], Type[float], Type[int], Type[complex], Type[bool]]"  [arg-type]
```