Implement provenance preserving method on NonNull

**Description**
 Add the `addr`, `with_addr, `map_addr` methods to the `NonNull` type,
 and map the address type to `NonZeroUsize`.

 **Motiviation**
 The `NonNull` type is useful for implementing pointer types which have
 the 0-niche. It is currently possible to implement these provenance
 preserving functions by calling `NonNull::as_ptr` and `new_unchecked`.
 The addition of these methods simply make it more ergonomic to use.

 **Testing**
 Added a unit test of a nonnull tagged pointer type. This is based on
 some real code I have elsewhere, that currently routes the pointer
 through a `NonZeroUsize` and back out to produce a usable pointer.

0 files changed, 0 insertions, 0 deletions