Implement PUBSUB SHARDCHANNELS and SHARDNUMSUB commands

[prateek-kumar-improving]

Description

Implement the PUBSUB SHARDCHANNELS and PUBSUB SHARDNUMSUB commands for PHP. Also missing in C#.

Note: PUBSUB CHANNELS, PUBSUB NUMSUB, and PUBSUB NUMPAT are already implemented via the $client->pubsub() method in valkey_glide_pubsub_introspection.c.

Commands

• PUBSUB SHARDCHANNELS — Lists active shard channels matching a pattern
• PUBSUB SHARDNUMSUB — Returns subscriber count for given shard channels

Reference

• https://valkey.io/commands/pubsub-shardchannels/
• https://valkey.io/commands/pubsub-shardnumsub/
• [EPIC] Valkey Commands Tracker valkey-glide#6292 — Commands Tracker