feat: add is_ variant methods to EdgeKind

[ss2165]

Closes #1767

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 15 lines in your changes missing coverage. Please review.

Project coverage is 86.58%. Comparing base (eef239f) to head (b14d6b9).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
hugr-core/src/types.rs	0.00%	15 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1768      +/-   ##
==========================================
- Coverage   86.62%   86.58%   -0.04%     
==========================================
  Files         180      180              
  Lines       32843    32858      +15     
  Branches    29750    29765      +15     
==========================================
  Hits        28449    28449              
- Misses       2758     2773      +15     
  Partials     1636     1636              

Flag	Coverage Δ
python	92.43% <ø> (ø)
rust	85.97% <0.00%> (-0.05%)	⬇️

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