chore: Fix violations of elided_named_lifetimes (#18330)

I compile Zed from nightly build pretty often and I've noticed that
we're getting a few hits on new rustc lint:
https://github.com/rust-lang/rust/pull/129207

Release Notes:

- N/A

crates/sum_tree/src/sum_tree.rs

@@ -345,7 +345,7 @@ impl<T: Item> SumTree<T> {
         Iter::new(self)
     }
 
-    pub fn cursor<'a, S>(&'a self, cx: &<T::Summary as Summary>::Context) -> Cursor<T, S>
+    pub fn cursor<'a, S>(&'a self, cx: &<T::Summary as Summary>::Context) -> Cursor<'a, T, S>
     where
         S: Dimension<'a, T::Summary>,
     {
@@ -358,7 +358,7 @@ impl<T: Item> SumTree<T> {
         &'a self,
         cx: &<T::Summary as Summary>::Context,
         filter_node: F,
-    ) -> FilterCursor<F, T, U>
+    ) -> FilterCursor<'a, F, T, U>
     where
         F: FnMut(&T::Summary) -> bool,
         U: Dimension<'a, T::Summary>,

crates/sum_tree/src/tree_map.rs

@@ -105,7 +105,7 @@ impl<K: Clone + Ord, V: Clone> TreeMap<K, V> {
         cursor.item().map(|item| (&item.key, &item.value))
     }
 
-    pub fn iter_from<'a>(&'a self, from: &'a K) -> impl Iterator<Item = (&K, &V)> + '_ {
+    pub fn iter_from<'a>(&'a self, from: &'a K) -> impl Iterator<Item = (&'a K, &'a V)> + 'a {
         let mut cursor = self.0.cursor::<MapKeyRef<'_, K>>(&());
         let from_key = MapKeyRef(Some(from));
         cursor.seek(&from_key, Bias::Left, &());