Find the reverse-replacements by strictly using single pass and maximal munch

[ztane]

I.e. if {{ cookiecutter.foo }} is substituted with car and {{ cookiecutter.bar }} with carpet the reverse mapping from carpet should be uniquely {{ cookiecutter.bar }} and never {{ cookiecutter.foo }}pet.

Likewise, the replacements should not target the jinja2 substitutions themselves; the previous code could have resulted in {{ {{ cookiecutter.project_name }}.foobar }} if the project name was cookiecutter :D

[ztane]

Hmm, seems to have a formatting issue but also mypy complains about re.Match not being typed as re.Match[bytes]. But the generic was introduced only in 3.9 :/