raise warning if any pretext-managed file does not match the version of pretext using it

[StevenClontz]

In https://github.com/PreTeXtBook/pretext-cli/issues/814 we had an issue where an author had 2.6-generated files, but was running 2.4.1 somehow. We could annotate our generated files with a version number and raise a warning if there's a mismatch (as long as they're being managed by PreTeXt).