message: Remove unused `split_cache` in `pane_grid`
diff: @@ -4,7 +4,6 @@ use crate::{
  Hasher, Point, Rectangle, Size,
  };
  -use std::cell::RefCell;
  use std::collections::HashMap;
  /// The state of a [`PaneGrid`].
  @@ -72,7 +71,6 @@ impl<T> State<T> {
  internal: Internal {
  layout,
  last_id,
  - split_cache: RefCell::new(None),
  action: Action::Idle { focus: None },
  },
  modifiers: keyboard::ModifiersState::default(),
  @@ -310,7 +308,6 @@ pub struct Internal {
  layout: Node,
  last_id: usize,
  action: Action,
  - split_cache: RefCell<Option<HashMap<Split, (Axis, f32, Rectangle)>>>,
  }
  #[derive(Debug, Clone, Copy, PartialEq, Eq)]
  