[C2] Optimize global chat

[ywarnier]

The new global chat is great, but inefficient. It doesn't take advantage of a moderating algorithm that existed in 1.11, which is to slow down the frequency of refreshes progressively:

• one request every one second for 5 seconds, then
• one request every 5 seconds for 30 seconds, then
• one request every 10 seconds for 120 seconds, then
• one request every 30 seconds for the rest of time

Also, the request itself takes about 640ms to return. This is too long. It probably uses too much memory as well. This should be super-focused on checking whether there's a new message for that person in the chat table.