Daemon plot_labels() for faster start (#9057)

* Daemon `plot_labels()` for faster start

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update train.py

Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>

Signed-off-by: Glenn Jocher <glenn.jocher@ultralytics.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

utils/general.py

@@ -622,7 +622,7 @@ def download(url, dir='.', unzip=True, delete=True, curl=False, threads=1, retry
     dir.mkdir(parents=True, exist_ok=True)  # make directory
     if threads > 1:
         pool = ThreadPool(threads)
-        pool.imap(lambda x: download_one(*x), zip(url, repeat(dir)))  # multi-threaded
+        pool.imap(lambda x: download_one(*x), zip(url, repeat(dir)))  # multithreaded
         pool.close()
         pool.join()
     else: