Backrefs

- **NEW**: Add support for Python 3.13 beta.

- **FIX**: Update project metadata to indicate Python 3.12 support.

- **NEW**: Officially support Python 3.12.

- **FIX**: Fix some flag issues in `bregex`.

- **NEW**: `\e` and `\h` have both been deprecated in 6.0. Please migrate to using `\x1b` and `\p{Horiz_Space}` in
their respective place.
- **FIX**: Fix flag issue with `sub` functions.

- **NEW**: Officially support Python 3.11.
- **NEW**: Add to Bre compatible custom Unicode properties `\p{Vert_Space}` and `\p{Horiz_Space}` that match Regex's new
custom properties. This helps to expose vertical space shorthand that was not previously present.