templates: add type hints to from_template / list_templates

[brendancol]

Closes #3542.

Adds type annotations to the two public functions in xrspatial/templates.py:

def from_template(name: str,
                  resolution: Optional[Union[float, Tuple[float, float]]] = None,
                  *, preserve: Optional[str] = None, backend: str = "numpy",
                  fill: float = np.nan,
                  chunks: Union[int, str, Tuple] = "auto") -> xr.DataArray:

def list_templates(kind: Optional[str] = None) -> Union[Dict[str, List[str]], List[str]]:

Both functions previously had no hints, while the analogous DataArray constructor generate_terrain and most public entry points (slope, aspect, curvature, proximity, zonal, classify) are annotated. This brings the templates surface in line.

Non-breaking: signatures and runtime behavior are unchanged. Verified from_template across all four backends (numpy, dask+numpy, cupy, dask+cupy) on a CUDA host.

Adds test_public_functions_have_type_hints, which asserts both functions carry a return annotation and a hint on every parameter. Full test_templates.py passes (64 tested).

The resolution parameter intentionally maps to attrs['res']; that naming is left as is (res is the array-contract attr name, resolution is the clearer constructor parameter).

Found by the api-consistency sweep (category 3).