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-datastruct/src/lru.rs

@@ -4,8 +4,10 @@
 //! allocated entries; here the entries live in a slab and are linked by
 //! index.
 
-use std::collections::HashMap as StdHashMap;
-use std::hash::{BuildHasher, Hash, RandomState};
+use std::{
+    collections::HashMap as StdHashMap,
+    hash::{BuildHasher, Hash, RandomState},
+};
 
 /// Create a HashMap for a key type that can be automatically hashed.
 /// If you want finer-grained control, use [`HashMap`] directly.