Remove CacheTrait::as_any_mut (#7833)

* Part of https://github.com/emilk/egui/issues/5876

No longer needed on modern MSRV

crates/egui/src/cache/cache_storage.rs

@@ -28,11 +28,13 @@ pub struct CacheStorage {
 
 impl CacheStorage {
     pub fn cache<Cache: CacheTrait + Default>(&mut self) -> &mut Cache {
-        #[expect(clippy::unwrap_used)]
-        self.caches
+        let cache = self
+            .caches
             .entry(std::any::TypeId::of::<Cache>())
-            .or_insert_with(|| Box::<Cache>::default())
-            .as_any_mut()
+            .or_insert_with(|| Box::<Cache>::default());
+
+        #[expect(clippy::unwrap_used)]
+        (cache.as_mut() as &mut dyn std::any::Any)
             .downcast_mut::<Cache>()
             .unwrap()
     }

crates/egui/src/cache/cache_trait.rs

@@ -1,11 +1,9 @@
 /// A cache, storing some value for some length of time.
 #[expect(clippy::len_without_is_empty)]
-pub trait CacheTrait: 'static + Send + Sync {
+pub trait CacheTrait: 'static + Send + Sync + std::any::Any {
     /// Call once per frame to evict cache.
     fn update(&mut self);
 
     /// Number of values currently in the cache.
     fn len(&self) -> usize;
-
-    fn as_any_mut(&mut self) -> &mut dyn std::any::Any;
 }

crates/egui/src/cache/frame_cache.rs

@@ -79,8 +79,4 @@ impl<Value: 'static + Send + Sync, Computer: 'static + Send + Sync> CacheTrait
     fn len(&self) -> usize {
         self.cache.len()
     }
-
-    fn as_any_mut(&mut self) -> &mut dyn std::any::Any {
-        self
-    }
 }

crates/egui/src/cache/frame_publisher.rs

@@ -54,8 +54,4 @@ where
     fn len(&self) -> usize {
         self.cache.len()
     }
-
-    fn as_any_mut(&mut self) -> &mut dyn std::any::Any {
-        self
-    }
 }

crates/egui/src/plugin.rs

@@ -120,13 +120,13 @@ impl PluginHandle {
     }
 
     fn typed_plugin<P: Plugin + 'static>(&self) -> &P {
-        (&*self.plugin as &dyn std::any::Any)
+        (self.plugin.as_ref() as &dyn std::any::Any)
             .downcast_ref::<P>()
             .expect("PluginHandle: plugin is not of the expected type")
     }
 
     pub fn typed_plugin_mut<P: Plugin + 'static>(&mut self) -> &mut P {
-        (&mut *self.plugin as &mut dyn std::any::Any)
+        (self.plugin.as_mut() as &mut dyn std::any::Any)
             .downcast_mut::<P>()
             .expect("PluginHandle: plugin is not of the expected type")
     }