6.1

A big update, this one.

- Moved to .NET 8.
- Updated viewport.
 - Data preparation also sees major gains (> 10x) from broad and deep use of multithreading across all areas.
 - Increased performance (> 2x) from moving data preparation into tasks and only updating buffers when required. More efficient drawing strategies were also deployed.
 - With assistance from the Veldrid maintainer, new approach resolves issues with mesa/GTK under newer Linux environments.
  - Currently, Vulkan does not seem to work well on Linux.
- GeoCore refinements:
 - Improved handling of complex layouts.
  - Previous code would read in irregular arrays, but would write a flattened representation, which was not ideal.
   - New approach centralizes the handling of array data to make the code less complex.
  - Repetition handling has been greatly improved and subject to extensive validation.
  - Improved handling of compressed layout data following some runtime changes in the platform.
  - Obscure bug in the box handling was found and addressed.
  - Correctness review across the code.
- Migration and expansion of test coverage.
- Enhancements for overlap/enclosure handling.
- Fixed numerous UI irritations, including lingering UI elements on tabs where they are not relevant.
- Unidirectional bias available, using Minkowski Sum, with before/after rotation option.
- The Mac platform is no longer supported due to no user interest and no hardware.