Ninst

- make `tkinter` optional (19)
- add preliminary `mcr` constants (19)
- misc build/test framework updates (19)
+ fix external PRs
+ update workflows
+ update pre-commit

- fix askdir user input refusal (18 <- [NiftyPET7](https://github.com/NiftyPET/NiftyPET/issues/7))

- misc framework updates (17)

- update `resources.py` (16)
+ add the scatter ring definition
+ add a tx projection constant consistent with `def.h`
- fix `dcm2niix` access permissions (16)
- minor framework updates (16)

- fix device ID inconsistency between NVML and CUDA (14)
- minor build/deploy updates

- use `miutil.web.urlopen_cached()` (13)
- use `miutil.fdio.extractall()` (13)
- fix `NiftyReg` on gcc9 (13)
- misc build & tests framework updates
+ parallel `cmake` builds
+ skip `devel` PRs