Support variable time array lengths

Chronify currently requires that all time arrays have the same length. This is fine for datasets based on a single [weather] year. It doesn't work across years because of leap years. The problem exists for datetime and index-time configurations.

Suppose a dataset like this:

• Years 2010 - 2020
• Index time, hourly
• 2012, 2016, 2020 will have 8784 indexes
• Other years will have 8760

1. What does the user specify for length in the time config?
2. How does chronify generate correct expected time index values?

The time configs need additional parameters to specify these behaviors. We can assume that the dataset will have a column that can be used to distinguish years (like "year" or "weather_year").