This avoids it ever mutating the underlying track (aka attempting to start
it). Resolves the one caveat mentioned in
aeef92fa710648d4a00edc523e13c17ac6104125.
The new implementation of `DecouplingClock` will not mutate the
underlying clock in any way (unless attempting to start it when
approaching from a negative time value).
This should be quite safe as a result.