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-vt/src/dcs.rs

@@ -2,8 +2,10 @@
 //! into a stream. The hook/put/unhook functions are meant to be called from
 //! the stream's dcsHook, dcsPut, and dcsUnhook functions, respectively.
 
-use crate::parser::Dcs;
-use crate::tmux::control::{Notification, Parser as TmuxParser};
+use crate::{
+    parser::Dcs,
+    tmux::control::{Notification, Parser as TmuxParser},
+};
 
 /// DCS command handler.
 #[derive(Debug)]