Fix RubyTest runner reliability

[trans]

Summary

• Fail explicit file requests that match nothing and runs that record no tests.
• Apply filters to top-level and nested tests, and count skipped tests and cases.
• Record case errors while continuing later tests; finish suite and test cleanup after errors.
• Repair hash reporter failure handling and output restoration.
• Fix --config, Testfile discovery, and the global assertionless setting.
• Add QED regression coverage and document the changed empty-run behavior.

Verification

• bundle exec rake test — 3 demos, 23 steps, 23 assertions; no failures or errors.
• CLI smoke checks for missing files, explicit --config, and automatic Testfile discovery.
• Focused checks for nested filtering, skips, case errors, hash reporter failures, and output restoration.