Backfill nearest neighbor outputs for single dates

[tiffanychu90]

• Trial several ways to put together the nearest neighbor script, including dask.map_partitions, itertuples, unpacking iterables, list comprehension, and the existing np.vectorize
• Use a dict to figure out the opposite direction to exclude for stop_primary_direction...move out of the loop, this is the only change that actually saves a couple of minutes
• Fix minor details: drop null shape geometries
• Backfill all the single dates for all 3 types of segments for the nearest neighbor output / delete stage2b outputs from GCS
• Epic - GTFS analytics pipeline performance improvements #1315