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/class/dialog.rs

@@ -4,8 +4,7 @@
 //! `adw::MessageDialog` fallback is not needed). Subclasses implement
 //! [`DialogImpl`] and may override `response` via `AlertDialogImpl`.
 
-use adw::prelude::*;
-use adw::subclass::prelude::*;
+use adw::{prelude::*, subclass::prelude::*};
 use gtk::glib;
 
 mod imp {