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/ipc/dbus.rs

@@ -1,9 +1,7 @@
 //! D-Bus helper for IPC (port of `apprt/gtk/ipc/DBus.zig`).
 
 use ghostty_apprt::ipc::{Error, Target};
-use gtk::gio;
-use gtk::glib;
-use gtk::prelude::*;
+use gtk::{gio, glib, prelude::*};
 
 /// A pending `org.gtk.Actions.Activate` call.
 pub struct DBus {