Drop support for ruby 3.1

[robertcheramy]

• [X] I have read and understood docs/Issues.md.

Is your feature request related to a problem? Please describe. Some dependencies of oxidized / oxidized-web dropped the support for ruby 3.1:

• haml => 7.0.0 (dependency of oxidized-web)
• git => 4.0.0 (dependency of oxidized for gitcrypt output)

Some code could be be simplified:

• https://github.com/ytti/oxidized/blob/3e3f6437bad0d38eac898a8a766d2d61bff74c08/lib/oxidized/hook.rb#L19-L21

Distribution support:

• Debian oldstable (bookworm) needs Ruby 3.1
• Debian stable (trixie) ships with Ruby 3.3
• Rockylinux 9 (Blue Onyx) supports ruby 3.1 and 3.3 (after module enable)
• Rockylinux 10 (Red Quarz) ships with ruby 3.3
• Ubuntu 24.04 (Noble Numbat) ships with ruby 3.2
• Older Ubuntu 22.04 (Jammy Jellyfish) ships with ruby 3.0

Dropping ruby 3.1 will have an impact on extentions:

• oxidized-web
• oxidized-script

Describe the solution you'd like The aim of this issue is to discuss if we should drop the support of ruby 3.1 and if yes, in which oxidized release.

Describe alternatives you've considered We will have to drop the support of ruby 3.1 in the end.

[robertcheramy]

Note - dropping ruby 3.1 means updating the installation instructions.

[robertcheramy]

I plan to discontinue support for Ruby 3.1 in version 0.36.0 if no one objects.