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/path.rs

@@ -1,5 +1,4 @@
-use std::io;
-use std::os::unix::fs::PermissionsExt;
+use std::{io, os::unix::fs::PermissionsExt};
 
 /// Equivalent of `std.fs.max_path_bytes` on Linux.
 const MAX_PATH_BYTES: usize = 4096;