fix: memory leak due to un-limited process usage

[SuicaLondon]

@hyiso Based on the issue of the high memory usage, and the suggestion @BTMuli provided. I added a new parameter to limit the maximum processes can run at the same time.

1. I have tested that using Process.kill helps reduce memory usage somewhat. As shown in the image below, macOS does not aggressively terminate processes on its own, so manual termination is necessary.

2. I tested it on a random open-source project and successfully reduced memory usage.

The default behaviour is the same (Does not set the process parameter).

If I added the --process 8.

And this is the memory usage of these two commands

3. I have covered it with both unit tests and integration tests.
4. I have updated the README.md

[hyiso]

Thanks for the great work on this PR!

[hyiso]

LGTM