custom shader animation can be set to "always" to always remain active

Fixes #1225

The `custom-shader-animation` configuration can now be set to "always"
which keeps animation active even if the terminal is unfocused.

src/config/Config.zig

@@ -815,15 +815,21 @@ keybind: Keybinds = .{},
 /// If true (default), the focused terminal surface will run an animation
 /// loop when custom shaders are used. This uses slightly more CPU (generally
 /// less than 10%) but allows the shader to animate. This only runs if there
-/// are custom shaders.
+/// are custom shaders and the terminal is focused.
 ///
 /// If this is set to false, the terminal and custom shader will only render
 /// when the terminal is updated. This is more efficient but the shader will
 /// not animate.
 ///
+/// This can also be set to "always", which will always run the animation
+/// loop regardless of whether the terminal is focused or not. The animation
+/// loop will still only run when custom shaders are used. Note that this
+/// will use more CPU per terminal surface and can become quite expensive
+/// depending on the shader and your terminal usage.
+///
 /// This value can be changed at runtime and will affect all currently
 /// open terminals.
-@"custom-shader-animation": bool = true,
+@"custom-shader-animation": CustomShaderAnimation = .true,
 
 /// If anything other than false, fullscreen mode on macOS will not use the
 /// native fullscreen, but make the window fullscreen without animations and
@@ -2079,6 +2085,15 @@ fn equalField(comptime T: type, old: T, new: T) bool {
     }
 }
 
+/// Valid values for custom-shader-animation
+/// c_int because it needs to be extern compatible
+/// If this is changed, you must also update ghostty.h
+pub const CustomShaderAnimation = enum(c_int) {
+    false,
+    true,
+    always,
+};
+
 /// Valid values for macos-non-native-fullscreen
 /// c_int because it needs to be extern compatible
 /// If this is changed, you must also update ghostty.h