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-bench/src/synthetic.rs

@@ -1,8 +1,9 @@
 //! Synthetic data generators (port of `ZIG/src/synthetic`): random bytes,
 //! UTF-8 and OSC sequences, used to feed the benchmarks.
-use ghostty_vt::string_encoding::url_percent_encode;
 use std::io::{self, Write};
 
+use ghostty_vt::string_encoding::url_percent_encode;
+
 /// xoshiro256++ (what Zig's `std.Random.DefaultPrng` is).
 #[derive(Debug, Clone)]
 pub struct Rng {
@@ -666,9 +667,10 @@ fn finished(r: io::Result<usize>) -> io::Result<bool> {
 
 #[cfg(test)]
 mod tests {
-    use super::*;
     use ghostty_vt::osc::Parser;
 
+    use super::*;
+
     const SEED: u64 = 0xC0FFEEEEEEEEEEEE;
 
     #[test]