fix: Support fractional refresh rates in video modes on macOS (#4191)

We were rounding the refresh rate before converting it to millihertz.

src/changelog/unreleased.md

@@ -254,3 +254,4 @@ changelog entry.
 - On Wayland, fixed a crash when consequently calling `set_cursor_grab` without pointer focus.
 - On Wayland, ensure that external event loop is woken-up when using pump_events and integrating via `FD`.
 - On Wayland, apply fractional scaling to custom cursors.
+- On macOS, fixed `VideoMode::refresh_rate_millihertz` for fractional refresh rates.

src/platform_impl/apple/appkit/monitor.rs

@@ -126,13 +126,12 @@ impl MonitorHandle {
         let modes = unsafe { CFRetained::cast_unchecked::<CFArray<CGDisplayMode>>(array) };
 
         modes.into_iter().map(move |mode| {
-            let cg_refresh_rate_hertz =
+            let cg_refresh_rate_hertz = unsafe { CGDisplayMode::refresh_rate(Some(&mode)) };
-                unsafe { CGDisplayMode::refresh_rate(Some(&mode)) }.round() as i64;
 
             // CGDisplayModeGetRefreshRate returns 0.0 for any display that
             // isn't a CRT
-            let refresh_rate_millihertz = if cg_refresh_rate_hertz > 0 {
+            let refresh_rate_millihertz = if cg_refresh_rate_hertz > 0.0 {
-                NonZeroU32::new((cg_refresh_rate_hertz * 1000) as u32)
+                NonZeroU32::new((cg_refresh_rate_hertz * 1000.0).round() as u32)
             } else {
                 refresh_rate_millihertz
             };