Svmbir

Changes include:
* Default to max_resolution=0 in prox mode
* Check prox_image input for valid shape
* Update Pillow version requirements

Includes fixes in setup.py for the conda-forge build.

- Update requirements with Pillow<=9.3 (9.4 is causing import fail on MacOS/x86_64)
- Update setup.py for MacOS builds

Changes include:

- This contains an adjustment to the thread limiter that will fix the divergent result presented in 268.

Changes include:

- Added support for Python 3.7; still supports Python 3.8-3.10
- Stop pinning to specific numpy (now supports numpy>=1.21)
- Update C code to normalize SV priority keys by effective SVDEPTH
- Update C code to limit threads on small problem size
- Minor clean up; allow interslice regularization =0.0
- Updated documentation for added fan beam geometry (curved, flat)

Changes include:
- support for python 3.8-3.10
- add support for flat-panel fan beam geometry
- add over-relaxation capability for pixel updates
- multi-resolution reconstruction is now default
- auto_sigma functions incorporate magnification
- documentation updates

This contains two fixes:

1. **CRITICAL** Fix in C code that crashes on macOS/arm64 (see https://github.com/HPImaging/sv-mbirct/issues/16)
2. Adds check for write permission before writing system matrix