query: should support multiple session IDs within one connection

[katrinafyi]

According to https://wiki.vg/Query, the session ID is intended to identify requests within a connection. As such, multiple session IDs should be handled correctly.

Within https://github.com/mcstatus-io/demo-server/blob/d86be2555327fdc0dfcc5e190af4b8d14d3d53c6/src/query/packets.go, the session ID is used as a key for the challenge token map so varying the session ID leads to an invalid challenge token.

The vanilla server instead keys its challenges by the connected socket.