feat(object-cache): add Relay as a supported object cache driver

[faisalahammad]

Description

Add support for the Relay PHP extension (relay.so) as a third object cache driver option alongside Memcached and Redis in LiteSpeed Cache settings.

Relay is a Redis-compatible, shared-memory PHP extension that provides an in-memory cache layer at the PHP process level. It is API-compatible with phpredis for all object caching calls this plugin uses (connect, pconnect, auth, select, get, set, del, flushDb, rawCommand).

Closes #906

Type of Change

• New feature (non-breaking change which adds functionality)
• Bug fix (fixes multisite multi-switch option casting in conf.cls.php)

Proposed Changes

1. src/base.cls.php:
   • Register O_OBJECT_KIND in _conf_multi_switch() to accept value 2 (Relay).
2. src/conf.cls.php:
   • Fix network_update() multi-switch check so integer values (0/1/2) are preserved instead of being cast to boolean.
3. src/object-cache.cls.php:
   • Change _cfg_method to integer representation (0 = Memcached, 1 = Redis, 2 = Relay).
   • Add _resolve_driver() and _driver_cls_exists() helper methods.
   • Update _connect() to instantiate \Relay\Relay for value 2, skip phpredis-only options, and validate PING responses ('PONG', '+PONG', true).
   • Route get(), set(), delete(), and flush() through Relay when selected.
   • Add \Exception catch block to safely catch \Relay\Exception (which does not extend \RedisException).
   • Make _redis_error() driver-aware for log messages and admin notices.
4. tpl/cache/settings_inc.object.tpl.php:
   • Add Relay extension status badge to the status display row.
   • Expand the Method radio switch to 3 options (Memcached, Redis, Relay).
   • Update jQuery port auto-fill logic so Relay (value 2) defaults to port 6379.

Verification & Testing

• PHPCS: Ran composer run sniff-check — 0 errors, 0 warnings (exit 0).
• PHP Lint: Verified syntax (php -l) on all modified files.
• Backward Compatibility: Existing sites using Memcached (0) or Redis (1) are unaffected. If Relay is selected but relay.so is not installed, class_exists() check keeps object cache safely disabled.