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-terminal/src/terminal/tests/p4.rs

@@ -1,6 +1,6 @@
+use ghostty_vt::{color::Rgb, sgr::Attribute as A};
+
 use super::*;
-use ghostty_vt::color::Rgb;
-use ghostty_vt::sgr::Attribute as A;
 
 const RED: Rgb = Rgb {
     r: 0xFF,