ENH: Initial pixi configuration

Initial [pixi](https://pixi.sh) configuration, supporting easy, reproducible builds for development and testing.

Cross-platform build and test configuration utilizing Ninja and
cross-platform conda-forge toolchains. And Python build and test
configuration. These are specified by `cxx` and `python` environments.

The following tasks are defined:

 - build           Build ITK
 - build-debug     Build ITK - Debug
 - build-debug-python Build ITK - Debug
 - build-python    Build ITK
 - build-release   Build ITK - Release
 - clean           Clean the repository
 - configure       Configure ITK
 - configure-debug Configure ITK - Debug
 - configure-debug-python Configure ITK Python - Debug
 - configure-python Configure ITK Python
 - configure-release Configure ITK - Release
 - test            Test ITK
 - test-debug      Test ITK - Debug
 - test-debug-python Test ITK Python - Debug
 - test-python     Test ITK Python
 - test-release    Test ITK - Release

.gitattributes

@@ -56,8 +56,11 @@ Modules/ThirdParty/GDCM/src/gdcm/Source/DataDictionary/privatedicts.xml hooks-ma
 Modules/Filtering/Denoising/include/itkPatchBasedDenoisingImageFilter.hxx hooks-max-size=120000
 Documentation/docs/releases/* hooks-max-size=300000
 Documentation/Art/* hooks-max-size=300000
+pixi.lock hooks-max-size=1000000
 
 # VNL-specific .gitattributes should go into Modules/ThirdParty/VNL/.gitattributes
 # GDCM-specific .gitattributes should go into Modules/ThirdParty/GDCM/src/gdcm/.gitattributes
 
 # HDF5-specific .gitattributes should go into Modules/ThirdParty/HDF5/.gitattributes
+# GitHub syntax highlighting
+pixi.lock linguist-language=YAML linguist-generated=true

.gitignore

@@ -46,3 +46,6 @@ Testing/Temporary/
 
 # CMake user presets
 CMakeUserPresets.json
+# pixi environments
+.pixi
+*.egg-info