Function source_walker 

pub fn source_walker(source: &Utf8Path) -> WalkBuilder

Build a source-tree walker that skips yui’s internal .yui/ directory.

.yui/backup/ can grow huge over time, and .yui/rendered/ (future) would also live here — neither is part of the user’s dotfiles, and walking them slows render / list / absorb-find by a lot. We also keep .gitignore / .ignore filtering disabled (git_ignore(false), ignore(false)) so a user’s unrelated ignore rules don’t swallow legitimate .tera / .yuilink files deeper in the tree.