fix: clippy warning unused_features

[AsakuraMizu]

No description provided.

[Copilot]

Pull request overview

This PR adjusts a crate-level feature gate in src/lib.rs to avoid triggering the unused_features clippy warning by only enabling doc_cfg in a documentation-specific configuration.

Changes:

• Replaced the unconditional #![feature(doc_cfg)] with #![cfg_attr(docsrs, feature(doc_cfg))] to avoid unused_features outside docs builds.

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[Copilot]

cfg_attr(docsrs, ...) relies on the docsrs cfg being set. A repo-wide search shows no place that sets/passes --cfg docsrs (e.g., in RUSTDOCFLAGS/RUSTFLAGS or package.metadata.docs.rs), so this feature gate will never be enabled in CI docs builds and may also trigger unexpected_cfgs warnings under -D warnings if check-cfg is active. Consider either switching to cfg_attr(doc, feature(doc_cfg)) (if you want it on any rustdoc build) or explicitly enabling/declaring docsrs (e.g., via Cargo.toml docs.rs metadata and/or the docs workflow flags / rustc check-cfg declarations).

Suggested change

	#![cfg_attr(docsrs, feature(doc_cfg))]
	#![cfg_attr(doc, feature(doc_cfg))]