Require Ruby >= 3.3 and update CI Ruby versions

[dduugg]

Summary

Ruby 3.2 is now EOL. This PR raises the minimum supported Ruby to 3.3 and refreshes the CI test matrix to the supported set (3.3 and 3.4).

Motivation: resolve Ruby version restrictions from rubyatscale/pack_stats#56, where supporting EOL Ruby forced older/vulnerable transitive dependencies.

Changes

• code_manifest.gemspec: required_ruby_version raised from >= 2.7 to >= 3.3 (preserving the Gem::Requirement.new style).
• .github/workflows/ci.yml: RSpec matrix now tests 3.3 and 3.4 (dropped EOL 3.0, 3.1, 3.2); head retained. Removed the now-stale '3.0' quoting comment.

Notes

• No bundle install was run and Gemfile.lock is unchanged.
• push_gem.yml (ruby-version: ruby) is intentionally left unchanged.
• Latest stable Ruby is 3.4.9; 3.5 is preview-only and not included.

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.