[rasterio] Accept int EPSG codes and any to_wkt provider in CRSInput (#16294)

`CRS.from_user_input` dispatches on a `to_wkt` method before checking any
concrete type, and reads a bare `int` as an EPSG code. Model the former as a
`_SupportsToWkt` Protocol rather than taking a dependency on pyproj.

Author: thomas-maschler

stubs/rasterio/rasterio/_typing.pyi

@@ -16,13 +16,19 @@ class _SupportsGeoInterface(Protocol):
     @property
     def __geo_interface__(self) -> Mapping[str, Any]: ...
 
+@type_check_only
+class _SupportsToWkt(Protocol):
+    def to_wkt(self) -> str: ...
+
 # A GeoJSON-like mapping, or any object exposing one through the
 # `__geo_interface__` protocol (e.g. shapely / geopandas geometries).
 # The runtime unwraps `__geo_interface__` before use, so both forms are
 # accepted anywhere a geometry is expected.
 Geometry: TypeAlias = Mapping[str, Any] | _SupportsGeoInterface  # noqa: Y047
 Colormap: TypeAlias = dict[int, tuple[int, int, int] | tuple[int, int, int, int]]
-CRSInput: TypeAlias = str | dict[str, str] | CRS
+# A WKT / PROJ string, an EPSG code, a PROJ dict, or any object exposing
+# `to_wkt` (e.g. a pyproj CRS). `CRS.from_user_input` normalizes all of them.
+CRSInput: TypeAlias = str | int | dict[str, str] | CRS | _SupportsToWkt
 FileOrBytes: TypeAlias = BinaryIO | bytes
 Indexes: TypeAlias = int | Sequence[int]
 NumType: TypeAlias = int | float