One of the challenges with the cursor work is that both the find and getMore commands have non-standard behaviors regarding timeouts. Currently, the maxTimeMS option is being set identically for every command, on the Protocol::Message class. In order to support per-command timeout behaviors, we need to move that to the OpMsg subclasses themselves.

Generally, this can be done with minimal hassle:

• Pass context to a new OpMsg by adding a parameter to Specifiable#initialize. (We need to be careful because Specifiable is also used on Operation classes; we might need a separate constructor for OpMsg subclasses). The OpMsgExecutable#execute methods are already being given the context, so it shouldn’t be hard to pass it through.
• Modify OpMsgBase#message so that it uses the context to apply the default timeout behavior to the command.