Refactor adapters to share more code and reduce boilerplate

[Totodore]

Currently there are three different remote adapters:

• Redis
• Postgres
• Mongodb

They each have a lot of common behavior that could be moved to socketioxide_core behind the remote_adapter feature flag.

We should make a little study on what can be factored-out. Here are the following things that I have in mind:

• packet encoding/decoding
• acknowledgement streams
• response handlers and multiplexing
• heartbeats

[LiamCarPer]

Hey man I looked into this issue and went through all three adapters. There's a lot of copy-paste
going on.
The AckStream + DropStream stuff is basically the same code three times with different types. The ResponseHandlers map + send_req/send_res/get_res pattern too. And the recv_broadcast, recv_rooms, recv_fetch_sockets etc. handlers all follow the same flow, just wired to different driver methods.
Postgres and MongoDB also share heartbeat logic (nodes_liveness, periodic emit, init handshake). Redis doesn't use it.
What I'm thinking:

• Move AckStream, DropStream, and ResponseHandlers into socketioxide_core behind the remote-adapter feature flag since those are straightforward to make generic
• Then a dispatch_request() helper that handles all the recv_* dispatch so each adapter just passes its decoded request and a response sender
• Heartbeat struct for the ones that need it

What stays in each adapter is the driver trait, channel setup (pubsub vs LISTEN vs change streams), and encoding (msgpack vs JSON + attachment table for postgres).
I'd start with AckStream + DropStream since they're the most copy-pasted and should be easy to extract without breaking anything. Does that sound like the right direction? If yes I'll open a draft PR so you can see the approach before I do the whole thing.