fix(sharded): SSUBSCRIBE smessageBuffer memory leak (#528)

[RoccoC]

This is a proposed fix for #528.

This pull request introduces a change to the sharded adapter's SSUBSCRIBE logic: Previously, for each dynamic channel/room, a unique listener was added to the client's smessageBuffer. This approach led to a large number of listeners (resulting in MaxListenersExceededWarning), especially in scenarios with many dynamic channels. Further, listeners were not being removed when unsubscribing, leading to a memory leak.

The new implementation replaces the multiple listeners with a single smessageBuffer listener. This listener is registered once and handles all dynamic channels by maintaining specific channel handlers in a Map. Listeners are added to this Map in SSUBSCRIBE and removed from the Map in SUNSUBSCRIBE.

Thanks for your review! 🙏

[darrachequesne]

@RoccoC awesome, thanks 👍