[Aryex]

Summary

Move the PubSub code from glide module to pubsub module, making it inline with how search module works.

Issue link

No linked issue. This is a focused organization change for the existing Pub/Sub implementation.

Changes

Pub/Sub files are now organized as:

lib/valkey/pubsub.rb # Pub/Sub entrypoint for imports
lib/valkey/pubsub/pubsub_message.rb
lib/valkey/pubsub/pubsub_state.rb
lib/valkey/pubsub/pubsub_receiver.rb
lib/valkey/commands/pubsub_commands.rb # Pub/Sub command API

require "valkey/pubsub" loads the Pub/Sub types and internal receiver without requiring the main client entrypoint. Tests and AGENTS.md now use the new namespace and paths.

Test also moved to reflect the new location.

Limitations

This PR only reorganizes Pub/Sub support. Search commands and types are unchanged.

Testing

• bundle exec rake test:unit (528 tests, 1,371 assertions, 0 failures)
• bundle exec rubocop (141 files, no offenses)
• Direct require "valkey/pubsub" check using Valkey::PubSub::PubSubMessage, PubSubState, and PubSubReceiver

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. No changelog entry is needed because these Pub/Sub types have not shipped; AGENTS.md is updated.
• Linters have been run (bundle exec rubocop) and pass.
• Destination branch is correct - main.