feat: Ensure packages always have modules at the root

[aborgna-q]

Followup to #1587.

Ensures that rust Packages only contain module-rooted hugrs. Returns errors at construction times if the condition is not met.
This required fixing hugr-cli, as it should be able to load both packages and arbitrary hugrs.
Added Package::from_hugr{,s} methods that try to wrap the hugrs if possible. We'll need these for tket2.

Packages are not on the spec yet, their description should include this restriction. See #1388.

This PR does only modify the (unpublished) API introduced in #1587, so I'm not marking it as breaking.

[codecov]

Codecov Report

Attention: Patch coverage is 88.52459% with 14 lines in your changes missing coverage. Please review.

Project coverage is 85.72%. Comparing base (c5b597d) to head (61aae85).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
hugr-core/src/package.rs	92.47%	5 Missing and 2 partials ⚠️
hugr-cli/src/lib.rs	76.00%	5 Missing and 1 partial ⚠️
hugr-cli/src/mermaid.rs	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##             main    #1589    +/-   ##
========================================
  Coverage   85.72%   85.72%            
========================================
  Files         136      136            
  Lines       24783    24891   +108     
  Branches    21719    21827   +108     
========================================
+ Hits        21244    21337    +93     
- Misses       2437     2446     +9     
- Partials     1102     1108     +6     

Flag	Coverage Δ
python	92.68% <ø> (ø)
rust	84.74% <88.52%> (+<0.01%)	⬆️

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[aborgna-q]

#1587 made some breaking changes. I'll try to fix them in a following PR, and replace them with #[deprecated]

edit: #1591

[doug-q]

Thanks!

I wish PackageOrHugr and Package had impl AsRef<[Hugr]>.

I think we should rename Package::validate to Package::update_validate for consistency.

[aborgna-q]

I renamed the update method. Note that this is a breaking release, but #1591 will take care of deprecating things.

[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_missing: pub enum variant removed or renamed ---

Description:
A publicly-visible enum has at least one variant that is no longer available under its prior name. It may have been renamed or removed entirely.
      ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
     impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.36.0/src/lints/enum_variant_missing.ron

Failed in:
variant CliError::Package, previously in file /home/runner/work/hugr/hugr/BASELINE_BRANCH/hugr-cli/src/lib.rs:47

--- failure inherent_method_missing: pub method removed or renamed ---

Description:
A publicly-visible method or associated fn is no longer available under its prior name. It may have been renamed or removed entirely.
      ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
     impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.36.0/src/lints/inherent_method_missing.ron

Failed in:
HugrArgs::get_package, previously in file /home/runner/work/hugr/hugr/BASELINE_BRANCH/hugr-cli/src/lib.rs:79

--- failure inherent_method_missing: pub method removed or renamed ---

Description:
A publicly-visible method or associated fn is no longer available under its prior name. It may have been renamed or removed entirely.
      ref: https://doc.rust-lang.org/cargo/reference/semver.html#item-remove
     impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.36.0/src/lints/inherent_method_missing.ron

Failed in:
Package::validate, previously in file /home/runner/work/hugr/hugr/BASELINE_BRANCH/hugr-core/src/package.rs:36