fix(model): avoid non abi-compatible pyo3 calls

[ss2165]

Wheel builds are failing when maturin tries to target PyPy because PyPy 3.10 doesn't support stable abi. pyo3 to_str() is not available on non-abi builds so fails. We can use the non-restricted to_cow() instead.

drive-by: use "release-py" profile to build wheels in maturin action

CI test: https://github.com/CQCL/hugr/actions/runs/19307683710

[codecov]

Codecov Report

❌ Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.40%. Comparing base (45dc3fc) to head (7473f16).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
hugr-model/src/v0/ast/python.rs	0.00%	5 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2679   +/-   ##
=======================================
  Coverage   83.40%   83.40%           
=======================================
  Files         264      264           
  Lines       51513    51513           
  Branches    46984    46984           
=======================================
  Hits        42962    42962           
  Misses       6167     6167           
  Partials     2384     2384           

Flag	Coverage Δ
python	91.32% <ø> (ø)
rust	82.63% <0.00%> (ø)

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[aborgna-q]

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