MAINT: General mainteance after the QMFlows 1.0.0b1 release

[BvB93]

A bunch of minor fixes in the wake of the 1.0.0b1 pre-release:

• Remove more deprecation leftovers
• Remove the ever-flaky Sphinx tests
• Add tests for the MacOS CP2K tests
• Add tests for the CP2k .psmp + mpi executable

[codecov]

Codecov Report

Merging #301 (8b19364) into master (7fac013) will increase coverage by 0.66%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #301      +/-   ##
==========================================
+ Coverage   80.28%   80.94%   +0.66%     
==========================================
  Files          43       43              
  Lines        2298     2299       +1     
  Branches      399      399              
==========================================
+ Hits         1845     1861      +16     
+ Misses        332      327       -5     
+ Partials      121      111      -10     

Impacted Files	Coverage Δ
src/qmflows/packages/_cp2k.py	90.90% <ø> (ø)
src/qmflows/packages/__init__.py	92.30% <100.00%> (+0.64%)	⬆️
src/qmflows/packages/_scm.py	68.92% <100.00%> (ø)
src/qmflows/parsers/_cp2k_basis_parser.py	98.18% <100.00%> (+3.63%)	⬆️
src/qmflows/test_utils.py	81.45% <100.00%> (+1.61%)	⬆️

... and 6 files with indirect coverage changes

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