feat: is_ext utility for checking equality against extension ops

[ss2165]

Open to bikeshedding on name of is_ext

left in an assert_eq that just uses cast directly as a comparison (this may not be worthwhile)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 87.29%. Comparing base (a38e58c) to head (5e9d7e1).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1499   +/-   ##
=======================================
  Coverage   87.29%   87.29%           
=======================================
  Files         126      126           
  Lines       21633    21638    +5     
  Branches    18662    18667    +5     
=======================================
+ Hits        18884    18889    +5     
  Misses       1979     1979           
  Partials      770      770           

Flag	Coverage Δ
python	92.72% <ø> (ø)
rust	86.43% <100.00%> (+<0.01%)	⬆️

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[ss2165]

Closing as I've convinced myself it's not useful.