feat(pubsub): pattern subscriptions, lazy variants and callback delivery

[Aryex]

Summary

This implement the advanced pubsub APIs per part 3 of the implementation plan.

Issue link

Related #135

Changes

The following APIs are added

Method	Request type
psubscribe(*patterns, timeout_ms: 0)	PSUBSCRIBE_BLOCKING (916)
punsubscribe(*patterns, timeout_ms: 0)	PUNSUBSCRIBE_BLOCKING (917)
subscribe_lazy(*channels)	SUBSCRIBE (911)
unsubscribe_lazy(*channels)	UNSUBSCRIBE (913)
psubscribe_lazy(*patterns)	PSUBSCRIBE (901)
punsubscribe_lazy(*patterns)	PUNSUBSCRIBE (908)

Callback subscriptions is also added:

Valkey.new(protocol: :resp3, pubsub: {
  subscriptions: { exact: ["news"] },
  callback: ->(message, context) { context.handle(message) },
  context: my_app_state
})

Limitations

• The six sharded verbs and publish(sharded: true) remain NotImplementedError (Part 4).
• get_subscriptions, the five pubsub_* introspection commands, and pubsub(subcommand, *args) remain NotImplementedError (Part 5), so the lazy verbs' documented "read back get_subscriptions to confirm" workflow is not yet available.
• No integration coverage in this PR — see Testing.
• validate_pubsub_callback! checks respond_to?(:call) only. A callable that does not respond to arity passes construction and then fails inside deliver, where the blanket rescue drops every message silently.

Testing

bundle exec rubocop — 124 files, no offenses.

bundle exec rake test:unit — 402 tests, 873 assertions, 0 failures (up from 366; 36 new).

• test/unit/glide/pubsub_test.rb: 15 new dispatch tests. Request type, argument order and string coercion for all six verbs; timeout coercion for the blocking pair (default 0 → "0", fractional truncated, sub-millisecond → "1", negative → ArgumentError); a parametrized regression guard that the four lazy verbs send no timeout argument; empty-list behavior per verb. The existing RESP2/nil-protocol sweep was extended to cover all six.
• test/unit/glide/pubsub_receiver_test.rb (new): 21 tests driving the retained ffi_handler proc directly with real FFI::MemoryPointer buffers, so no server is needed. Queue mode unchanged; callback ordering; arity-1 vs arity-2 dispatch; a raising callback neither propagates nor kills the receiver; pop/try_pop raise in callback mode; ffi_handler object identity retained; non-message push kinds dropped; embedded NUL preserved; and the ArgumentError validation paths.

bundle exec ruby -Itest -Ilib test/integration/standalone/valkey_test.rb — 216 tests, 13 failures, all pre-existing lib_name / client_info_tag assertions unrelated to Pub/Sub, identical to the base branch's baseline. No Pub/Sub test fails.

Integration coverage is deliberately not in this PR. Nothing yet exercises psubscribe → publish → #pattern, the lazy verbs' eventual delivery, or callback mode against a live server. test/integration/valkey/pubsub_test.rb now runs in both standalone and cluster (via TestClusterPubSub), so those tests must be mode-safe; they will follow in a separate PR rather than being added unrun.

bundle exec rake test:cluster has not been run against this stack.

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.