Update docs, comments to nudge timing with monotonic clock

[openbl]

What

Update docs and comments to encourage people to use the monotonic clock.

Why

The docs and comments show use of Time.now for timing interactor descendants. However, Time.now can suffer from "discontinuous jumps" that are solved by using the system's monotonic clock.¹

[gaffneyc]

Thanks for the pull request (and sorry for it sitting so long). Do you know if CLOCK_MONOTONIC is available across all operating systems and architectures that Ruby runs on?

Looking at the examples, they're focusing on how to use hooks rather than what's in the code example itself. While using CLOCK_MONOTONIC is the right way to do it I'm not sure changing it meaningfully adds to the example as Time.now is usually good enough. The example could have used Benchmark.realtime { ... } to calculate total runtime which uses CLOCK_MONOTONIC under the hood but that would have obscured the use of interactor.call.

[gaffneyc]

While using CLOCK_MONOTONIC is the right way to do it I think it just complicates the examples for little gain.

Going to close this but open to an alternative change that uses a different example to show the same concept.