Improve performance of `os.walk()`

There are a couple of minor performance improvements possible in os.walk():

• We don't need to manually pump the os.scandir iterator, given we handle exceptions from next() like exceptions from scandir() itself, i.e. by ignoring the problematic directory and moving on. We can use a for loop like filthy casuals.
• In bottom-up mode, we can handle exceptions from entry.is_symlink() in the same block as those from entry.is_dir(), which avoids a few temporary variables.
• In top-down mode, we can call os.path.join() once on a parent directory rather than for each child path.

Linked PRs

• gh-119186
• gh-119473
• gh-119573
• gh-119750
• gh-121431
• gh-121432
• gh-121433
• gh-121435

os.walk() のエントリポイントから始め、os.scandir()、entry.is_dir()、entry.is_symlink()、os.path.join() の使用箇所を調査してください。変更を加える前に、関連付けられた PR gh-119186、gh-119473、gh-119573、gh-119750、gh-121431、gh-121432、gh-121433、gh-121435 を確認してください。提案されたパフォーマンス改善によって例外処理と走査の動作が維持されれば完了です。