Require Ruby >= 3.3 and update CI Ruby versions

[dduugg]

Summary

Bumps the minimum supported Ruby version to 3.3 (Ruby 3.2 is now EOL) across the gem's version requirement, linting target, and local Ruby pin.

Changes

• packs.gemspec: required_ruby_version bumped from Gem::Requirement.new('>= 3.2') to Gem::Requirement.new('>= 3.3').
• .rubocop.yml: AllCops/TargetRubyVersion bumped from 3.2 to 3.3.
• .ruby-version: bumped from 3.2.2 to 3.4.9 (latest stable Ruby).

Notes

• CI/CD workflows (.github/workflows/ci.yml, cd.yml) delegate to the rubyatscale/shared-config reusable workflows and define no inline Ruby version matrix, so no workflow changes were needed.
• mise.toml already pins Ruby to 3.4, so it was left unchanged.
• No README/docs minimum-version statements reference an old Ruby version.
• No changes to Gemfile.lock; bundle install was not run.

Motivation

Resolves the Ruby version restrictions from rubyatscale/pack_stats#56, where supporting EOL Ruby forced older/vulnerable transitive dependencies.

Bundler

Also bumps BUNDLED WITH in Gemfile.lock to bundler 4.0.15 (latest). The previously pinned bundler version crashes on Ruby head (NameError: uninitialized constant Pathname::SEPARATOR_PAT) — see this failing run. Pinning the current bundler resolves it.