Fix clippy warnings and doc(cfg) attributes

[leighmcculloch]

What

Replace #[cfg_attr(feature = "doc", doc(cfg(...)))] with #[cfg_attr(doc, doc(cfg(...)))] in src/escape.rs and src/unescape.rs. Add #![cfg_attr(doc, feature(doc_cfg))] to src/lib.rs to enable the nightly doc_cfg feature when building docs. Replace the let...else in Escape::next with the ? operator.

Why

feature = "doc" is not a defined Cargo feature, so the doc(cfg(feature = "alloc")) annotation never activated and rustdoc output omitted feature-gate hints on alloc-gated items. The let...else triggered clippy::question_mark.

Close #11

[chatgpt-codex-connector]

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[Copilot]

Pull request overview

This PR addresses Clippy warnings and fixes non-activating rustdoc feature-gating annotations by adjusting cfg_attr usage for doc(cfg(...)) and simplifying iterator code in Escape::next.

Changes:

• Switch cfg_attr(feature = "doc", ...) to cfg_attr(doc, ...) for doc(cfg(feature = "alloc")) annotations.
• Enable doc_cfg (nightly) when building docs via a crate-level cfg_attr.
• Replace a let ... else with ? in Escape::next to satisfy clippy::question_mark.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
src/lib.rs	Adds crate-level gating intended to enable nightly doc_cfg for doc builds.
src/escape.rs	Updates doc(cfg(...)) activation condition and applies a small Clippy-driven simplification in Escape::next.
src/unescape.rs	Updates doc(cfg(...)) activation condition for the alloc-gated API.

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[mootz12]

[picky] is the RUSTDOCFLAGS="--cfg doc" needed anymore?