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/formatter/tests/p3.rs

@@ -1,6 +1,7 @@
-use super::*;
 use ghostty_vt::modes::Mode;
 
+use super::*;
+
 /// Format the screen with the given extras, returning output and pin map.
 fn screen_vt(t: &Terminal, mutate: impl FnOnce(&mut ScreenFormatter<'_>)) -> (String, Vec<Pin>) {
     let mut pin_map: Vec<Pin> = Vec::new();