feat(topology/spectral/hom): Spectral maps (#12228)
Define spectral maps in three ways:
* `is_spectral_map`, the unbundled predicate
* `spectral_map`, the bundled type
* `spectral_map_class`, the hom class
The design for `is_spectral_map` matches `continuous`. The design for `spectral_map` and `spectral_map_class` follows the hom refactor.
