fix(release): keep test model workspace-only

[danieleades]

What changed

• mark fenwick-model as a workspace-only crate
• use it as a path-only development dependency from arithmetic-coding

Why

The 0.5.0 release has been stuck since the release PR merged. Release-plz excludes dev-dependencies from its topological publish order (release-plz/release-plz#2697), so it tries to package arithmetic-coding before publishing fenwick-model 0.1.1. Cargo then rejects the package because that dev-dependency version does not exist on crates.io.

fenwick-model is internal test support and does not need an independent public release. Keeping it path-only removes the registry dependency and prevents this ordering bug on future releases.

Merging this PR also provides a fresh push for release-plz to publish the already-prepared arithmetic-coding 0.5.0 release.

Validation

• cargo test --all-features
• cargo fmt --all --check
• cargo package -p arithmetic-coding --allow-dirty

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 87.57%. Comparing base (b1501bf) to head (9e6ec66).
⚠️ Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #118   +/-   ##
=======================================
  Coverage   87.57%   87.57%           
=======================================
  Files          11       11           
  Lines         483      483           
=======================================
  Hits          423      423           
  Misses         60       60           

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[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Retain fenwick-model for packaged test targets

When Cargo packages this crate, a path-only dev-dependency is omitted from the normalized Cargo.toml; consequently the published crate has no fenwick-model dependency. Its included tests/fuzz.rs, benches/sherlock.rs, and Fenwick examples import that crate, so running cargo test, cargo bench, or building all examples from the unpacked crates.io source will fail to resolve it. Keep a published dependency version or exclude the affected targets from the package.

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