gpui: Make inactive frame throttling configurable (#62628)

# Objective

I am building an [app](https://github.com/nolight132/sonora) with GPUI,
and the current animation throttling implementation does not quite meet
its requirements. I needed the window to stay at a smooth framerate when
unfocused to display lyrics, which was not possible at the time without
modifying GPUI’s frame scheduling behavior. I understand that this is
not a problem for Zed, but I believe making this behavior a field in
`WindowOptions` could be beneficial for other programs going forward.

## Solution

Added a field to `WindowOptions` struct which controls the minimum
interval between animation frames while the window is inactive
(documented). Kept the default value GPUI currently uses.

## Testing

- Ran `gpui/src/examples/animation.rs` with different presets - works as
expected. Zed compiles. One thing worth noting: this setting does not
guarantee the window refreshes at this exact interval, as frames are
still paced by the compositor. For granular FPS control, a helper
function is needed. I have decided to keep it simple and use the
existing logic.
- Tested on NixOS x86_64, Niri.

## Self-Review Checklist:

- [x] I've reviewed my own diff for quality, security, and reliability
- [x] Unsafe blocks (if any) have justifying comments
- [x] The content adheres to Zed's UI standards
([UX/UI](https://github.com/zed-industries/zed/blob/main/CONTRIBUTING.md#uiux-checklist)
and
[icon](https://github.com/zed-industries/zed/blob/main/crates/icons/README.md)
guidelines)
- [ ] Tests cover the new/changed behavior (the default didn't change,
tests still pass)
- [x] Performance impact has been considered and is acceptable (no
performance impact unless explicitly set)

## Showcase

Before (unfocused):
<img width="1280" height="802" alt="image"
src="https://github.com/user-attachments/assets/e3302c1d-4f4a-4503-96a2-0bf24e28096c"
/>

After (unfocused with `inactive_frame_interval` set to 16ms):
<img width="1450" height="972" alt="image"
src="https://github.com/user-attachments/assets/1183adf1-2da1-42d5-8e97-f4ad7a31b783"
/>

---

Release Notes:

- Added `WindowOptions::inactive_frame_interval` for configuring
animation frame throttling on inactive GPUI windows.

crates/gpui/src/platform.rs

@@ -1827,6 +1827,11 @@ pub struct WindowOptions {
     /// Leave this `false` for windows that rely on AppKit's native titlebar dragging.
     pub app_owns_titlebar_drag: bool,
 
+    /// The minimum interval between animation frames while the window is inactive.
+    ///
+    /// Set to `None` to disable inactive-window animation frame throttling.
+    pub inactive_frame_interval: Option<Duration>,
+
     /// Whether the window should be resizable by the user
     pub is_resizable: bool,
 
@@ -1971,6 +1976,7 @@ impl Default for WindowOptions {
             kind: WindowKind::Normal,
             is_movable: true,
             app_owns_titlebar_drag: false,
+            inactive_frame_interval: Some(Duration::from_micros(33_333)),
             is_resizable: true,
             is_minimizable: true,
             display_id: None,

crates/gpui/src/window.rs

@@ -1340,6 +1340,7 @@ impl Window {
             kind,
             is_movable,
             app_owns_titlebar_drag,
+            inactive_frame_interval,
             is_resizable,
             is_minimizable,
             display_id,
@@ -1557,7 +1558,7 @@ impl Window {
                 {
                     None
                 } else if !active.get() && !input_rate_tracker.borrow_mut().is_high_rate() {
-                    Some(Duration::from_micros(33333))
+                    inactive_frame_interval
                 } else if let Some(ThermalState::Critical | ThermalState::Serious) = thermal_state {
                     Some(Duration::from_micros(16667))
                 } else {