[droundy]

CI on master has been failing since before #68 (the #67 merge failed the same way). This PR fixes it.

Rust 1.70 jobs: parking_lot_core (through dashmap) and zmij (through serde_json) now need Rust 1.71. This raises rust-version and both CI matrices to 1.71. cargo test on 1.71 still couldn't build, because the criterion dev-dependency needs 1.80. criterion now sits behind a new benchmarks feature, which only the get_container bench requires.

Check (stable): This job was being cancelled by fail-fast, which hid failures in its later steps:

• --features intern32, intern and arena without std hit the crate's own compile_error! requiring std or spin. Those steps now add spin.
• intern32 didn't build without std. It used std:: paths, a deepsize bound that wasn't feature-gated, and the container module and append-only-vec without enabling them.

Docs: Making criterion optional means --all-features would build it on nightly, where clap fails. docs.rs and the CI docs job now list their features explicitly instead.

Three of the four commits are cherry-picked from the scaling-0.9 branch (#66): a3d4fd8, 2a44d7a and 31ba3bb. The docs commit's message and comment were adjusted to fit master. The MSRV commit mirrors that branch's approach, but its benchmarks feature only enables criterion here. That should keep the later merge of scaling-0.9 simple.

Tested locally on 1.71.0 and stable:

• Every Check step passes. The x86_64-unknown-none and thumbv6m-none-eabi steps were run on the host target, since those targets aren't installed here.
• cargo test passes on 1.71.
• cargo test --all-features -- --test-threads=1 passes.
• The nightly docsrs cargo doc passes with -Dwarnings.

Not fixed here: benches/bench.rs was already failing to build on master, because the arc-interner dependency it uses isn't enabled by the bench feature. No CI job builds the benches.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 80.22%. Comparing base (213e597) to head (807abec).

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #69      +/-   ##
==========================================
- Coverage   80.61%   80.22%   -0.39%     
==========================================
  Files          11       11              
  Lines        1852     1851       -1     
==========================================
- Hits         1493     1485       -8     
- Misses        359      366       +7     

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