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-core/tests/e2e_bindings.rs

@@ -6,8 +6,10 @@ use std::fmt::Write as _;
 
 mod common;
 use common::*;
-use ghostty_apprt::action::{Action, GotoSplit, SplitDirection};
-use ghostty_apprt::structs::Clipboard;
+use ghostty_apprt::{
+    action::{Action, GotoSplit, SplitDirection},
+    structs::Clipboard,
+};
 use ghostty_input::Key;
 
 #[test]