drop rails 6.1/7.0 support, bump required ruby to 3.1, add rails 8.0 to appraisals

[modosc]

this is a major version bump to 6.0.0.

1. drop support for rails-6.1 / rails-7.0 - new minimum version is rails-7.1
2. bump minimum ruby version to 3.1.0 in preparation for rails-7.2
3. relax rails dependencies to allow for rails-7.2 and rails-8.0
4. fix Appraisals branch for rails-7.2
5. add rails-8.0 to Appraisals

[chaadow]

This is more rails main/edge rather than 8.0, because it can be 8.1, 8.2 9.0 etc. It represents the "future of rails".

[chaadow]

I do understand the lower bound limit requirement.

However making an upper bound limit will always make it a hassle for people running on edge or unreleased version. (or recently released version, but you forgot to bump the dependency)

And even if let's say 8.1.0 gets released, people will be blocked by your gem to update to rails, forcing them to :

• fork the repo and remove this upper bound
• OR if forking is not a possibility, simply copy paste the code of this gem and include it in their app

My point is, since you have an appraisal that targets rails main/edge, you'll have a lot of opportunities when you release patch/minor fixes to catch bugs earlier in Github CI.
==> making your gem more future proof
==> and removing the need for this limiting upper bound