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-os/src/temp_dir.rs

@@ -1,9 +1,11 @@
 //! Creates a temporary directory at runtime that can be safely used to
 //! store temporary data and is destroyed on drop.
 
-use std::io;
-use std::os::unix::fs::DirBuilderExt;
-use std::path::{Path, PathBuf};
+use std::{
+    io,
+    os::unix::fs::DirBuilderExt,
+    path::{Path, PathBuf},
+};
 
 use crate::file::alloc_tmp_dir;