`ls`: Investigate printing performance

In seq, we found that directly calling stdout.write_all(str.as_bytes())? is quite a bit faster than using format to do the same operation: write!(stdout, "{str}")?. https://github.com/uutils/coreutils/pull/7562

ls uses a lot of write!(..., "{}", ..)?; patterns. Would be nice to know if switching to write_all would improve performance.

Had a very quick look at samply output, and printing dominate more of the runtime in long format outputs (e.g. ls -l), so maybe it'd be good to start investigating that use case.

For reference, we're doing a bit worse than coreutils:

$ cargo build -r -p uu_ls && taskset -c 0 hyperfine --warmup 3 -L ls target/release/ls,ls "{ls} -lR .git"
    Finished `release` profile [optimized] target(s) in 0.12s
Benchmark 1: target/release/ls -lR .git
  Time (mean ± σ):      32.5 ms ±   0.8 ms    [User: 18.7 ms, System: 13.5 ms]
  Range (min … max):    31.2 ms …  34.4 ms    84 runs
 
Benchmark 2: ls -lR .git
  Time (mean ± σ):      23.7 ms ±   1.5 ms    [User: 11.3 ms, System: 12.0 ms]
  Range (min … max):    23.0 ms …  38.6 ms    114 runs

Summary
  ls -lR .git ran
    1.37 ± 0.10 times faster than target/release/ls -lR .git

Start in the ls implementation by locating its write!(..., "{}", ..)? calls and compare them with seq's direct stdout.write_all pattern. Build the uu_ls release binary and run the provided hyperfine command against ls -lR .git; done means determining whether the output path improves performance and documenting the benchmark result.