feat: Python bindings for hugr-model.

[zrho]

This PR introduces Python bindings to hugr-model. On the Python side, we have dataclasses that mirror the model AST. On the Rust side, these classes are converted into the Rust AST structure. Using that, we can generate the text and binary representation.

[hugrbot]

This PR contains breaking changes to the public Rust API.
Please deprecate the old API instead (if possible), or mark the PR with a ! to indicate a breaking change.

cargo-semver-checks summary

[codecov]

Codecov Report

Attention: Patch coverage is 24.65582% with 602 lines in your changes missing coverage. Please review.

Project coverage is 82.55%. Comparing base (6bd7665) to head (fb1ac5f).

Files with missing lines	Patch %	Lines
hugr-model/src/v0/ast/python.rs	0.00%	246 Missing ⚠️
hugr-py/src/hugr/model/export.py	9.66%	215 Missing ⚠️
hugr-model/src/v0/mod.rs	0.00%	78 Missing ⚠️
hugr-py/src/hugr/tys.py	44.26%	34 Missing ⚠️
hugr-py/src/hugr/model/__init__.py	90.44%	13 Missing ⚠️
hugr-py/src/hugr/val.py	43.75%	9 Missing ⚠️
hugr-py/src/hugr/hugr/base.py	42.85%	4 Missing ⚠️
hugr-py/src/hugr/std/collections/array.py	75.00%	1 Missing ⚠️
hugr-py/src/hugr/std/float.py	66.66%	1 Missing ⚠️
hugr-py/src/hugr/std/int.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1959      +/-   ##
==========================================
- Coverage   83.73%   82.55%   -1.19%     
==========================================
  Files         209      212       +3     
  Lines       39266    40061     +795     
  Branches    35937    36265     +328     
==========================================
+ Hits        32879    33071     +192     
- Misses       4541     5144     +603     
  Partials     1846     1846              

Flag	Coverage Δ
python	85.69% <40.85%> (-6.35%)	⬇️
rust	82.22% <1.51%> (-0.75%)	⬇️

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