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-build-data/src/vim.rs

@@ -2,8 +2,10 @@
 
 use std::fmt::Write as _;
 
-use crate::chunks_vim::{C0, C1, C2, C3, C4};
-use crate::config_fields;
+use crate::{
+    chunks_vim::{C0, C1, C2, C3, C4},
+    config_fields,
+};
 
 pub const FTDETECT: &str = C0;
 pub const FTPLUGIN: &str = C1;