SimRate should support stopping with rate=0

[jshook]

The new SimRate rate limiter should be robust enough to "stop" an activity without breaking.
If the rate is initialized or set to 0, then it should effectively block indefinitely, but warn the user if it is stopped for a suspiciously (60 seconds) long period of time, and ultimately fail if a safety timeout passes (10 minutes). These safety checkpoints should be configurable.