Realtime only has a single socket even with different endpoints

### 👟 Reproduction steps

1. Create two Clients, and for each, create a Realtime.
2. Attempt to subscribe on each, possibly to different things.

Explicit example:
val clientA = Client().setEndpoint("http://localhost:8080/v1").setProject("1234")
val clientB = Client().setEndpoint("http://localhost:8088/v1").setProject("5678")

val realtimeA = Realtime(clientA).subscribe(...)
val realtimeB = Realtime(clientB).subscribe(...)

### 👍 Expected behavior

It should create one socket per Client, or at most per endpointRealtime.

If I have multiple Client objects connected to different backends, I should be able to have a separate socket to each.

Simply changing
```
class Realtime ... {
private companion object {
private var socket: RealWebSocket? = null
```

to
```
private val sockets: Map = mutableMapOf()
```

and making appropriate thread-safe changes to the few places sockets are created/destroyed would address this.

### 👎 Actual Behavior

It shares a single socket across all Client/Realtimes, as it puts the socket on a private companion object.

Thus when I create realtimeB and call subscribe, it will close the socket, and create a new socket to localhost:8088 but try to merge all the requests for updates together. It's possible there are different users on each backend, etc.

### 🎲 Appwrite version

Version 1.8.x

### 💻 Operating system

Linux

### 🧱 Your Environment

This is Kotlin using io.appwrite:sdk-for-android:11.4.0

Note that this is an unusual scenario to have multiple clients to multiple backends, but I'm designing a highly-resilient, client-driven multiple-backend project that can keep multiple backends in sync, so it's a requirement for my project.

### 👀 Have you spent some time to check if this issue has been raised before?

- [x] I checked and didn't find similar issue

### 🏢 Have you read the Code of Conduct?

- [x] I have read the [Code of Conduct](https://github.com/appwrite/.github/blob/main/CODE_OF_CONDUCT.md)