Clean up unsupported Ruby versions and remove unnecessary files

It looks like the repository still includes code and configurations for Ruby versions that are no longer maintained.
To make the project easier to maintain, how about removing support for those outdated versions and cleaning up related files?

This could include things like:

- Removing old Ruby versions from Gemfile, and CI configs
- Deleting version-specific patches or compatibility code
- Cleaning up redundant or unused files

I’d be happy to help with a PR if this sounds good!

Start by reviewing the Gemfile and CI configurations to identify the Ruby versions still supported, then locate any version-specific patches or compatibility files referenced by the repository. Confirm the project’s maintained Ruby-version policy before removing outdated entries and files, and verify that the CI configuration still covers the supported versions.

Written by the indexing model from the issue text.