style: apply nightly rustfmt import grouping across the workspace

rustfmt.toml sets group_imports, imports_granularity and imports_layout,
which are nightly-only; agents formatted with stable rustfmt, which
ignored them. This is a formatting-only pass with `cargo +nightly fmt`.

Test Plan:
- cargo clippy --workspace --all-targets -- -D warnings
- cargo test --workspace

crates/ghostty-apprt-gtk/src/ext/actions.rs

@@ -1,9 +1,6 @@
 //! GAction helpers (port of `apprt/gtk/ext/actions.zig`).
 
-use gtk::gio;
-use gtk::glib;
-use gtk::glib::prelude::*;
-use gtk::prelude::*;
+use gtk::{gio, glib, glib::prelude::*, prelude::*};
 
 fn g_action_name_is_valid(name: &str) -> bool {
     !name.is_empty()

crates/ghostty-apprt-gtk/src/ext/mod.rs

@@ -6,12 +6,9 @@
 pub mod actions;
 pub mod slice;
 
+use gtk::{glib, glib::prelude::*, prelude::*};
 pub use slice::StringList;
 
-use gtk::glib;
-use gtk::glib::prelude::*;
-use gtk::prelude::*;
-
 /// Get the first ancestor of `widget` of type `T`.
 pub fn get_ancestor<T: IsA<gtk::Widget>>(widget: &impl IsA<gtk::Widget>) -> Option<T> {
     widget.ancestor(T::static_type()).and_downcast::<T>()

crates/ghostty-apprt-gtk/src/ext/slice.rs

@@ -20,9 +20,10 @@ impl StringList {
 
 #[cfg(test)]
 mod tests {
-    use super::*;
     use gtk::glib::prelude::*;
 
+    use super::*;
+
     #[test]
     fn string_list_create_and_destroy() {
         let list = StringList::create(&["hello", "world"]);