Preserve keyword arguments across options and builders

[OskarEichler]

Summary

Preserve keyword arguments through Uber's option and builder forwarding layers on Ruby 3 and 4. This covers generated method/instance-exec wrappers, Options#evaluate/#eval, Builder#build!/Builders#call, and the still-shipped deprecated Options::Value helpers and evaluate alias.

The guarded Ruby ruby2_keywords mechanism retains the existing *args signatures and positional-hash behavior without introducing runtime syntax newer than the documented Ruby floor. User-provided direct Procs and Callable objects retain their identity.

Reproduction

require 'uber/options'
context = Object.new
def context.pick(required:); required; end
Uber::Option[:pick].call(context, required: 7)
Uber::Options.new(value: :pick).evaluate(context, required: 7)

Both calls previously raise ArgumentError on Ruby 3.2/4.0. They now return 7 and {value: 7}. Explicit positional hashes are not promoted to keywords; missing required keywords still raise. Keyword-only instance-exec lambdas and builder declarations fail similarly before the patch.

Verification

• Existing master baseline and this isolated branch: bundle exec rake test, 45 tests / 50 assertions, zero failures/errors/skips, Ruby 4.0.6 / Minitest 4.7.5.
• 4,202 focused forwarding checks on Ruby 3.2.11 and 4.0.6: required/empty/string-key keywords, positional hashes, Proc/Callable identity, legacy helpers and alias, nil execution context, static values and builder non-inheritance.
• Release-based combination with the separate unused-reference cleanup: existing suite passes on both Rubies; 2,750 additional inheritance/delegation boundary checks pass. Package retains all 25 paths and compared metadata; eight runtime files compile on both Rubies. Two pre-existing Lint offenses remain unchanged.
• Downstream Representable 3.2.0, baseline/fixed: 544 tests / 700 assertions, zero failures/errors, three existing skips on Ruby 3.2.11. Ruby 4 retains the same eight legacy inspection-format failures, zero errors and three skips. Existing tests are unchanged; external tooling supplies its old MiniTest alias and ruby-prof 1.7 API.
• Three alternating local YJIT process pairs show no observed call-path regression in this bounded positional workload (100,000 Proc calls ~0.0099→0.0097s; method calls ~0.0084→0.0083s). This is not a production throughput claim.

Compatibility / limitations

No intended breaking changes to documented APIs. Calls that previously lost explicit keywords now deliver them to their target. Positional arguments, explicit positional Hashes, empty keywords, static returns, private-method dispatch and unwrapped callable identity retain their behavior.

No new or modified checked-in tests. Ruby 1.9.3–3.1, JRuby, Windows and Linux were not executed locally. The keyword-marker calls are guarded for Ruby versions where the methods do not exist. Main's unrelated test/CI changes are not included in the 0.1.0 consumer backport.