feat: Packages do not include the hugr extensions by default

[aborgna-q]

Closes #2185, by shifting the responsibility to the user.

It also helps greatly reduce payload size, as we don't encode the prelude extension anymore :)

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.97%. Comparing base (0f78fab) to head (a065ee1).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2187      +/-   ##
==========================================
- Coverage   81.97%   81.97%   -0.01%     
==========================================
  Files         229      229              
  Lines       39948    39930      -18     
  Branches    36047    36029      -18     
==========================================
- Hits        32749    32734      -15     
+ Misses       5371     5368       -3     
  Partials     1828     1828              

Flag	Coverage Δ
python	85.64% <ø> (ø)
rust	81.58% <100.00%> (-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_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/v0.41.0/src/lints/enum_variant_missing.ron

Failed in:
variant PackageValidationError::MissingExtension, previously in file /home/runner/work/hugr/hugr/BASELINE_BRANCH/hugr-core/src/package.rs:135