Landice feature request: adaptive time stepper adjust to stream output times

[matthewhoffman]

Currently, the landice core has a config config_adaptive_timestep_force_interval that can be used to cause the adaptive time stepper in take a smaller step to hit some specified interval. This can be matched to stream output_interval to ensure you get output at an exact time. However, if you have multiple or complicated streams, or simply forget to sync this value, you won't get this behavior.

With additional logic, it would be possible to force the adaptive timestepper to 'hit' every stream output exactly. That behavior could be the default behavior, because I can't imagine a case where that is undesired.

Design: Loop over stream alarms and get earliest next ring time.