Solve warnings

[eval]

Fixes #1384, #1424, #1572

Before: https://github.com/mikel/mail/actions/runs/7384712114/job/20088103249#step:5:8

[sebbASF]

Given that these mostly come from generated files, it might be better to just ignore them as suggested here:

https://dev.to/qortex/ruby-suppress-those-warnings-you-can-t-do-anything-about-6ie

[eval]

While an easy option (for us), I think it's better in this case to not ship a transitive dependency for downstream users. Something the most popular gems using warning-gem also don't seem to do (ie it's a development dependency).

[skipkayhil]

This looks like an incomplete version of #1551. All of those parser files are generated by rake ragel, so modifying them by hand is not a good idea in my opinion.

[eval]

All of those parser files are generated by rake ragel, so modifying them by hand is not a good idea in my opinion.

@skipkayhil you're right, closing this one.