Spack issues tracker

[garth-wells]

Spack package issues to resolve. Fixes to be made in spack/spack-packages but tracking here.

• JIT via py-cffi requires py-setuptools. Should this go into the FFCx and/or DOLFINx spec?
• Remove the Boost +filesystem+program_options+timer options (the add-ons are no longer used by DOLFINx).
• For fenics-dolfinx, PETSc and SLEPc are optional (disabled by default, which is good Spack practice), but py-petsc4py is a dependency for py-fenics-dolfix. This means we can get the Python interface with petsc4py but the backend without PETSc (similarly for SLEPc).
• No py-slepc4py option for py-fenics-dolfix.
• Add no_cache=True to version for development versions (all FEniCS packages).
• Deprecate older versions.