refactor!: remove unused dependencies

[ss2165]

found using cargo-machete

no easy way to remove unused entries from the workspace Cargo.toml

BREAKING CHANGE: Removed some unused dependencies from hugr-llvm test-utils feature.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.71%. Comparing base (929edb6) to head (ceebd2d).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1935   +/-   ##
=======================================
  Coverage   83.71%   83.71%           
=======================================
  Files         196      196           
  Lines       37533    37533           
  Branches    34346    34346           
=======================================
  Hits        31422    31422           
  Misses       4328     4328           
  Partials     1783     1783           

Flag	Coverage Δ
python	92.34% <ø> (ø)
rust	82.91% <ø> (ø)

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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 feature_missing: package feature removed or renamed ---

Description:
A feature has been removed from this package's Cargo.toml. This will break downstream crates which enable that feature.
      ref: https://doc.rust-lang.org/cargo/reference/semver.html#cargo-feature-remove
     impl: https://github.com/obi1kenobi/cargo-semver-checks/tree/v0.39.0/src/lints/feature_missing.ron

Failed in:
feature pathsearch in the package's Cargo.toml
feature serde in the package's Cargo.toml
feature typetag in the package's Cargo.toml
feature serde_json in the package's Cargo.toml

[ss2165]

@doug-q please check the llvm removals are valid

[doug-q]

Yes looks good, thanks!

[doug-q]

Apparently this is a breaking change though, awkward