chore: Bump Rust version to 1.86 (#28021)

Closes #ISSUE

Release Notes:

- N/A

crates/gpui/src/key_dispatch.rs

@@ -488,7 +488,7 @@ impl DispatchTree {
             let (bindings, _) = self.bindings_for_input(&input[0..=last], dispatch_path);
             if !bindings.is_empty() {
                 to_replay.push(Replay {
-                    keystroke: input.drain(0..=last).last().unwrap(),
+                    keystroke: input.drain(0..=last).next_back().unwrap(),
                     bindings,
                 });
                 break;

crates/gpui/src/platform/mac/metal_renderer.rs

@@ -1211,7 +1211,7 @@ fn build_path_rasterization_pipeline_state(
 
 // Align to multiples of 256 make Metal happy.
 fn align_offset(offset: &mut usize) {
-    *offset = ((*offset + 255) / 256) * 256;
+    *offset = (*offset).div_ceil(256) * 256;
 }
 
 #[repr(C)]