perf: cli walks with tidy_walk
The CLI's own queue gives way to tidy_walk. On macOS, the XML corpus, 6,784 files in 4,203 folders, goes from about 167 to 130 ms; the other corpora stay within a few tenths of a ms. Writes now share the I/O threads, and an unreadable folder is an error instead of skipped.
Parentee918a8
2 files changed+44-161
StackedSplit