feat: Operation and constructor declarations in hugr-model

[zrho]

This PR adds the ability to declare custom operations and constructors (so static types, runtime types, constraints, etc.) to hugr-model. In the case of operations this is used for deduplication when exporting.

[codecov]

Codecov Report

Attention: Patch coverage is 78.37838% with 48 lines in your changes missing coverage. Please review.

Project coverage is 85.77%. Comparing base (fed74b5) to head (33e180e).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
hugr-core/src/import.rs	45.00%	13 Missing and 9 partials ⚠️
hugr-model/src/v0/text/parse.rs	74.46%	0 Missing and 12 partials ⚠️
hugr-model/src/v0/text/print.rs	78.57%	3 Missing and 6 partials ⚠️
hugr-model/src/v0/binary/read.rs	82.60%	0 Missing and 4 partials ⚠️
hugr-core/src/export.rs	98.21%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1605      +/-   ##
==========================================
+ Coverage   85.62%   85.77%   +0.14%     
==========================================
  Files         136      136              
  Lines       24929    25114     +185     
  Branches    21855    22040     +185     
==========================================
+ Hits        21346    21541     +195     
+ Misses       2476     2425      -51     
- Partials     1107     1148      +41     

Flag	Coverage Δ
python	92.45% <ø> (ø)
rust	84.84% <78.37%> (+0.17%)	⬆️

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[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

--- failure enum_variant_added: enum variant added on exhaustive enum ---

Description:
A publicly-visible enum without #[non_exhaustive] has a new variant.
      ref: https://doc.rust-lang.org/cargo/reference/semver.html#enum-variant-new
     impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.36.0/src/lints/enum_variant_added.ron

Failed in:
variant RegionKind:Module in /home/runner/work/hugr/hugr/PR_BRANCH/hugr-model/src/v0/mod.rs:390
variant Operation:DeclareConstructor in /home/runner/work/hugr/hugr/PR_BRANCH/hugr-model/src/v0/mod.rs:349
variant Operation:DeclareOperation in /home/runner/work/hugr/hugr/PR_BRANCH/hugr-model/src/v0/mod.rs:357

[zrho]

CI indicates a breaking change, but the change is confined to the model which is considered unstable. Also while patch coverage is slightly low, this PR overall slightly improves test coverage.