Use System.TimeProvider to control time

[yaakov-h]

This PR introduces use of TimeProvider (hooray for net8.0) to control time.

This can be configured via SteamConfiguration and allows for time to be slowed, sped up, paused, skipped, etc. to make some functions easier to test.

[yaakov-h]

System.Threading.Tasks.Dataflow doesn't seem to support this just yet so I can't easily hook it in to callback timeouts. I think.

[xPaw]

System.Threading.Tasks.Dataflow doesn't seem to support this just yet

Is this for WaitForCallback( TimeSpan timeout )? Can it be worked around by testing WaitForCallbackAsync( CancellationToken cancellationToken = default ) instead?