Add initial minimal SNAX target integration

[compor]

This PR:

• Adds support for SNAX cluster targets. Execution is guarded by the detection of snax-mlir in $PATH:

• initial CMake/Snakemake support for SNAX

• dummy SNAX kernel example

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The below are obsolete after discussion with @tobiasgrosser where he suggested minimal PRs.

TODO

• sort out pixi and venv environments
• proper minimal kernel that exercises OpenGEMM
• properly select OpenGEMM
• fix or augment current runtime for SNAX