Replaces the `indexOfFirst` linear scan over the unmerged incoming messages with a `HashMap` mapping message IDs to their index. This reduces the time complexity of the server message reconciliation loop from O(N^2) to O(N). Additionally, `removeAt()` calls on the unmerged list (which carry an O(N) penalty due to array shifting) were replaced by setting matched indices in a `MutableList<ChatMessage?>` to `null`.
M57
0724d0104d