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/string_map.rs

@@ -3,9 +3,10 @@
 //!
 //! Port of `ZIG/src/terminal/StringMap.zig`. Regex matching uses Oniguruma
 //! (the `onig` crate), like Ghostty.
-use crate::{page_list::Pin, selection::Selection};
 use onig::{MatchParam, Regex, Region, SearchOptions};
 
+use crate::{page_list::Pin, selection::Selection};
+
 /// Retry budget for StringMap regex searches.
 ///
 /// Units are Oniguruma retry steps (internal backtracking/retry counter),