Fix concurrency issue in SocketServer and address deprecations

[ramkrishna-xyz]

This PR replaces mutableMapOf with ConcurrentHashMap for resumableSessions in SocketServer.kt. This prevents ConcurrentModificationException during session resumption and cleanup. It also adds @Suppress("DEPRECATION") to PlayerRestHandler to reduce build noise.

[pryzmian]

I feel like this was made with AI

[ramkrishna-xyz]

@pryzmian what made you think so

[topi314]

do you have an actual instance of a ConcurrentModificationException happening?

[ramkrishna-xyz]

While we haven't seen an actual ConcurrentModificationException crash in the logs yet, I went ahead and fixed the resumableSessions map anyway.
The original code was using a standard mutableMapOf, which isn't thread-safe. Since both the WebSocket thread (handling connections) and the background executor (handling session timeouts) touch that same map, it was a guaranteed race condition waiting to happen. I've swapped it to a ConcurrentHashMap to make it thread-safe and prevent those random crashes before they actually hit us in production.

[ramkrishna-xyz]

@ToddyTheNoobDud the message was indeed ai generated because my english is like very bad so we will be in a serious type discussion here so I used ai to enhance my pull request message