This is part of the ["stackless"](#23299) change. I'm splitting it out into a separate PR because we need it for some work on sharding types.
Changes:
1. Rename `at_least_vspace` to `to_tangent_type` since that's what we always meant by it. `at_least_vspace` was always a bad name (sorry!) but it makes even less sense when you can have a special tangent type for a primal types that's already a vector space itself.
2. Replace `Zero.from_value` with `Zero.from_primal_value`, which does the required primal-type-to-tangent-type conversion.
3. Add `to_tangent_type` calls in various other places they're missing.
4. Remove non-support for float0 in custom deriviatives?
5. [Optional, WIP] Reinstate some checks that had been skipped over, presumably because of these bugs. (We'll see how far I get with it. Might end up being a separate PR.)
PiperOrigin-RevId: 676115753
Notable changes:
* use PEP 585 type names
* use PEP 604 type union syntax where `from __future__ import annotations` is present.
* use f-strings in more places.
* remove redundant arguments to open().
... in preparation for paring down `jax.core`'s exported symbols.
Also includes a few import fixups along the way, and a TODO comment to avoid an
import cycle in `_src/dtypes.py`.
PiperOrigin-RevId: 496024782
