Add downgrade compat action, bump minimal versions

[m-fila]

Adding downgrade compat action to check if minimal versions from Project.toml actually works. https://github.com/julia-actions/julia-downgrade-compat
The julia-actions/julia-downgrade-compat@v2 seems to be unstable now, using julia-actions/julia-downgrade-compat@v1

Bumped minimal version of aqua
Bumped minimal version of Julia and standard lib to current lts - we were claiming support for 1.9 but never actually check it

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.22%. Comparing base (b6356d3) to head (0b24cde).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #210   +/-   ##
=======================================
  Coverage   80.22%   80.22%           
=======================================
  Files          21       21           
  Lines        1315     1315           
=======================================
  Hits         1055     1055           
  Misses        260      260           

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[graeme-a-stewart]

Thanks @m-fila !