Changes

Refactor MSC params and add Wentzel VI params and data (#1129)

* Add Wentzel VI data

- Move common MSC data into separate structs
- Import geom_factor
- Check imported Wentzel VI data in test

* Add Wentzel VI params and MSC params interface

* Move common MSC params to physics

* Add helper class for constructing MSC params and address other feedback

* Remove geometry factor (currently unused)

* Fix test for float

* Change fact --> factor

* Add min/max energy methods to XsCalculator

Add spack-based workflow to add all supported Geant4 versions to CI (#1149)

* Add note about pull requests
* Show ccache stats even on failure
* Add spack-based CI build
* Add spack build to push/pr
* Mark failing builds as experimental
* Fix missing compiler/version from matrix
* Use patched geant4 in upstream spack
* Use only celer buildcache
* Shorten padded length
* Don't push the buildcache...
* Load version information to fix examples

Fix Geant4 build from 10.5–10.7 and example build for 11.1 onward (#1152)

* Add additional components in CeleritasConfig
* Remove obsolete requirement in CeleritasConfig
* Fix downstream (example) build with Geant4 11.1+
* Fix build for Geant4 10.5–10.7
* Fix example execution for Geant4@11.1+
* Add geant4 compatibility ranges
* Remove experimental status from geant builds

Rename `Wentzel` model to `CoulombScattering` and add em/params subdirectory (#1154)

* Rename Wentzel model classes to CoulombScattering

* Move em params to subdirectory

* Move MscParamsHelper to params/detail and fix namespace

Construct `ScintillationParams` based on the scintillation by particle type input flag.

Expand Scintillation test harness

Few fixes and improvements

- Fix Doxygen build error
- Add `scintillation_by_particle()` boolean in `ScintillationData` to
  verify which sampling method should be used; Improve documentation
- Use CELER_NOT_IMPLEMENTED whenever scintillation particle data is
  passed to the scintillation pre-generator and generator.
- Improve test

Fixup

Minor fix; Revert clang-format change in GeantImporter

Remove Interp type; Improve separation between material/particle import

Fix ScintillationData operator bool; minor reorg

Fix test units; Update operator bools; Fix ScintillationParams bug

Throw CELER_NOT_IMPLEMENTED at construction time; clean up;