core: rename PipelinePassSpec to ArgSpec for future frontends and targets

[superlopuh]

Subset of #5702.

[codecov]

Codecov Report

❌ Patch coverage is 94.87179% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 86.34%. Comparing base (583e55b) to head (91e5e9c).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
xdsl/utils/arg_spec.py	95.31%	1 Missing and 2 partials ⚠️
xdsl/utils/exceptions.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #5703   +/-   ##
=======================================
  Coverage   86.34%   86.34%           
=======================================
  Files         406      406           
  Lines       57732    57746   +14     
  Branches     6707     6708    +1     
=======================================
+ Hits        49848    49861   +13     
- Misses       6325     6326    +1     
  Partials     1559     1559           

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