QSV got too busy, so Claude modernized XSV

xsv was a revelation when it came out 10 years ago. It's a rust-based CSV tool. Lately people are recommended to use QSV, also rust-based, but incredibly (too much) feature rich. I worked with Claude to modernize XSV and add a few key features like --compress and --flexible... and also upgrade the underlying rust csv lib, whose 2018 version was known to hang on certain weird input.