Add support for OPT_REPLY_LITERAL

[prateek-kumar-improving]

PHPRedis has a configuration option OPT_REPLY_LITERAL that controls whether Redis "+OK" responses are returned as:

• String "OK" (when OPT_REPLY_LITERAL is enabled)
• Boolean true (when OPT_REPLY_LITERAL is disabled - the default)

This is set at runtime:
$redis->setOption(Redis::OPT_REPLY_LITERAL, false);

[KIvanow]

Hey! I took a shot at this after working on a previous PR with some C changes.
I've added OPT_REPLY_LITERAL support with setOption()/getOption() methods. When enabled, commands that return OK will return the string "OK" instead of boolean true.
PR: #120
Quick usage:

$client->setOption(ValkeyGlide::OPT_REPLY_LITERAL, true);
$result = $client->set('key', 'value'); // Returns "OK" instead of true

I tried to follow the PHPRedis approach but would really appreciate feedback on whether I got it right. Happy to make adjustments!