[Ruby][CI] Build precompiled gems for Ruby 4.0

[dewolfe]

What does this PR accomplish?

Adds Ruby 4.0 to the precompiled optify-config gem matrix.

The cross-build currently receives stable Ruby versions from fetch-ci-data but explicitly excludes Ruby 4.0. This removes that exclusion, so the existing cross-gem job builds Ruby 3.3, 3.4, and 4.0 extensions for:

• aarch64-linux
• arm64-darwin
• x86_64-linux

It also bumps the Ruby gem from 1.23.1 to 1.23.2. A new version is required because RubyGems will not allow the existing 1.23.1 platform artifacts to be replaced with packages containing an additional Ruby 4 extension.

Validation

• Confirmed the current CRuby stable-version feed contains 3.3, 3.4, 4.0, and head
• Workflow YAML parses successfully
• bundle check passes
• Ruby test suite: 51 tests, 710 assertions, 0 failures
• The 1.23.2 source gem builds successfully with the expected metadata
• Fork workflow run passed and cross-built the Ruby 4 extension for all three target platforms

The fork workflow packaged lib/optify_ruby/4.0/optify_ruby.* in the arm64-darwin, aarch64-linux, and x86_64-linux gems. Publishing was skipped because the run was not on main.

Why is this change necessary?

Ruby 4 source compatibility was added in #175, but the published platform gems still contain extensions only for Ruby 3.3 and 3.4 and declare required_ruby_version < 3.5.dev.

Ruby 4 applications therefore have to force the generic source gem and install Rust plus libclang in every development, CI, staging, and production build environment.

Publishing Ruby 4 platform artifacts removes that requirement and lets Bundler use the normal platform-specific gem.