Support automatic time binning

[domoritz]

It would vibe great if Mosaic had a way to bin time fields by time units (month, day etc) similar to https://vega.github.io/vega-lite/docs/timeunit.html and bin automatically by the most appropriate time unit.

Previous discussion at #283 (comment)

[domoritz]

@hamilton wrote a blog post about a query to determine the smallest time unit used in some data which could be useful for heuristics here as well: https://www.hamiltonulmer.com/smallest-timegrain-heuristic/.

[jheer]

Mosaic does support time binning. First, one can directly use existing DuckDB date part methods like quarter, month, dayofweek, etc. To bin a date without changing the type (resulting in a JS Date object in the browser), mosaic-sql includes the methods dateMonth, dateMonthDay, and dateDay. I agree that a method for automatically determining a "nice" binning unit could be helpful!

p.s. FWIW the bin transform supports temporal values as well, but treats them as numbers, currently without consideration for nice units.

[derekperkins]

Not sure if this would fall under Mosaic or DuckDB, but it would also be nice to handle day of week alignment when binning, for MoM and YoY