logiguard fork: GPUI xdg-activation keyboard-focus serial fix

Single-commit orphan branch: full zed-industries/zed @ 8c74db0 source tree
with a 3-file patch applied (no upstream history).

Patch (crates/gpui_linux/src/linux/wayland/):
  - serial.rs: add SerialKind::KeyboardEnter
  - client.rs: store wl_keyboard.enter serial; add latest_serial_of()
  - window.rs: activate() uses keyboard-enter serial (Mutter focus gate)

Mutter honors window activation only when the token carries the keyboard-
focus serial from wl_keyboard.enter; GPUI used a stale mouse-press serial.
See docs/tray-window-focus-wayland.md in logiguard.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/collab/src/executor.rs

@@ -0,0 +1,39 @@
+use std::{future::Future, time::Duration};
+
+#[cfg(feature = "test-support")]
+use gpui::BackgroundExecutor;
+
+#[derive(Clone)]
+pub enum Executor {
+    Production,
+    #[cfg(feature = "test-support")]
+    Deterministic(BackgroundExecutor),
+}
+
+impl Executor {
+    pub fn spawn_detached<F>(&self, future: F)
+    where
+        F: 'static + Send + Future<Output = ()>,
+    {
+        match self {
+            Executor::Production => {
+                tokio::spawn(future);
+            }
+            #[cfg(feature = "test-support")]
+            Executor::Deterministic(background) => {
+                background.spawn(future).detach();
+            }
+        }
+    }
+
+    pub fn sleep(&self, duration: Duration) -> impl Future<Output = ()> + use<> {
+        let this = self.clone();
+        async move {
+            match this {
+                Executor::Production => tokio::time::sleep(duration).await,
+                #[cfg(feature = "test-support")]
+                Executor::Deterministic(background) => background.timer(duration).await,
+            }
+        }
+    }
+}