fix: docs.rs build failure (doc_auto_cfg removed)

[matanlurey]

Same root cause as ixy's 0.6.0 -> 0.6.1 patch (ixy#8): docs.rs builds with a recent nightly where #![feature(doc_auto_cfg)] has been removed (merged into doc_cfg, rust-lang/rust#138907), so gem's 0.1.0 docs.rs build fails outright with:

error[E0557]: feature has been removed
  --> src/lib.rs:63:29
   |
63 | #![cfg_attr(docsrs, feature(doc_auto_cfg))]
   |                             ^^^^^^^^^^^^ feature has been removed

Fix

Switch to #![feature(doc_cfg)], matching grixy's and ixy's fix for the identical issue. Verified locally with the nightly toolchain and --cfg docsrs -Z unstable-options, matching docs.rs's own build invocation:

RUSTDOCFLAGS="--cfg docsrs -Z unstable-options" rustup run nightly cargo doc --all-features --no-deps

Bumped to 0.1.1 (patch, docs-only fix, no API change). Verified cargo build (default), cargo build/clippy/fmt/test/doc --all-features, and cargo package all clean.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

📢 Thoughts on this report? Let us know!