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

src/main.rs

@@ -5,8 +5,7 @@
 //! `ghostty-cli`; otherwise the configuration is loaded by the GTK runtime
 //! and the terminal application is run with the real core.
 
-use std::process::ExitCode;
-use std::rc::Rc;
+use std::{process::ExitCode, rc::Rc};
 
 use ghostty_apprt::ipc;
 use ghostty_apprt_gtk::{adw_version, gtk_version};