doc: enable doc_cfg

src/osu/gradual_difficulty.rs

@@ -49,6 +49,7 @@ use super::{
 ///     // ...
 /// }
 /// ```
+#[cfg_attr(docsrs, doc(cfg(feature = "gradual")))]
 pub struct OsuGradualDifficulty {
     pub(crate) idx: usize,
     mods: u32,

src/osu/gradual_performance.rs

@@ -89,6 +89,7 @@ use super::{OsuGradualDifficulty, OsuPerformanceAttributes, OsuScoreState};
 /// // attempting to process further objects will return `None`.
 /// assert!(gradual_perf.next(state).is_none());
 /// ```
+#[cfg_attr(docsrs, doc(cfg(feature = "gradual")))]
 #[derive(Debug)]
 pub struct OsuGradualPerformance<'map> {
     difficulty: OsuGradualDifficulty,