[Aryex]

Summary

Add Valkey 9.0 DELIFEQ support as delifeq(key, value). The method deletes a key only when its value exactly matches the comparison value and returns a Boolean result.

Issue link

Closes Add DELIFEQ command support.

Changes

• Adds the public string command, YARD documentation, changelog entry, and request type 1523. Comparison values are stringified with to_s, matching existing Ruby command conventions.
• Adds unit coverage for request construction and conversion, integration coverage for matching, nonmatching, non-string, binary, and pipeline behavior, and shared imperative MULTI and EXEC Boolean conversion coverage.
• Adds initial Ruby testing guidelines in docs/TESTING.md and links them from the AGENTS.md context retrieval table.

Limitations

DELIFEQ requires Valkey 9.0. Imperative MULTI and EXEC coverage is skipped in cluster mode because cluster transactions are not supported.

Testing

• git diff --check
• bundle exec ruby -Itest -Ilib test/unit/commands/string_commands_test.rb: 4 runs, 7 assertions
• bundle exec rake test:unit: 515 runs, 1,339 assertions
• SKIP_TLS_TESTS=true bundle exec rake test:standalone: 1,102 runs, 56,537 assertions
• SKIP_TLS_TESTS=true bundle exec rake test:cluster: 1,055 runs, 135,633 assertions
• Targeted standalone and cluster DELIFEQ integration tests
• Targeted imperative MULTI and EXEC Boolean conversion test: 1 run, 2 assertions
• bundle exec rubocop --cache false: 139 files inspected, no offenses
• Current GitHub CI RuboCop check passes

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to an issue.
• Commit message describe your changes
• Commits are signed off (git commit -s) per the DCO.
• Tests are added or updated.
• CHANGELOG.md and documentation files are updated.
• Linters have been run (bundle exec rubocop) and pass.
• Destination branch is correct - main.