Function ripGrepFileCount

* Stream-count lines from `rg --files` without buffering stdout. * * On large repos (e.g. 247k files, 16MB of paths), calling `ripGrep()` just * to read `.length` materializes the full stdout string plus a 247k-element * array. This counts newline bytes per chunk instead; peak memory is one * s

(
  args: string[],
  target: string,
  abortSignal: AbortSignal,
)