Streamline how resampling over DST transitions is handled for non-instantaneous sensor data

[Flix6x]

Since #118 we have a nice function to resample events for instantaneous data. This util function doesn't check for a specific sensor resolution, yet though. It may work well for non-instantaneous sensor data, too. We should find out, and either expand the test cases if it works, or assert that the sensor resolution is zero.

Specifically, I expect this work would touch:

• The fast-track downsampling logic, under downsample_beliefs_data_frame
• The fast-track upsampling logic, involving a reindex
• The logic for resampling instantaneous sensor data, under resample_instantaneous_events