(data) further clean

(data) clean too short files, strip yaml front matter

Require readme to be found during cleaning.

(debug) wrong source file changed.

(data) better filtering

(optim) faster rebuild

(format) format

(data) Exclude repo by name substring

Filtering data further

refactor: reorganize repository filtering into separate clean/ module with metadata and content filters

(rename) data_util to data_stats