feat: Special cased array, float and int constants in hugr-model export

[zrho]

This PR special cases the import/export of array, float and int constants so that they are represented as terms in hugr-model. This representation is a lot more efficient to handle than the encoding as JSON. In the future we should do this for all constants.

[codecov]

Codecov Report

Attention: Patch coverage is 78.84615% with 22 lines in your changes missing coverage. Please review.

Project coverage is 86.56%. Comparing base (be3961d) to head (39dafb9).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
hugr-core/src/import.rs	58.49%	10 Missing and 12 partials ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #1857    +/-   ##
========================================
  Coverage   86.55%   86.56%            
========================================
  Files         195      195            
  Lines       35584    35686   +102     
  Branches    32397    32499   +102     
========================================
+ Hits        30800    30891    +91     
+ Misses       3012     3010     -2     
- Partials     1772     1785    +13     

Flag	Coverage Δ
python	92.34% <ø> (ø)
rust	85.99% <78.84%> (+0.01%)	⬆️

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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/v0.38.0/src/lints/enum_variant_added.ron

Failed in:
variant Term:Float in /home/runner/work/hugr/hugr/PR_BRANCH/hugr-model/src/v0/mod.rs:724
variant Term:FloatType in /home/runner/work/hugr/hugr/PR_BRANCH/hugr-model/src/v0/mod.rs:730

[ss2165]

🚀

[ss2165]

thanks