Is your feature request related to a problem? Please describe.
https://docs.geopandas.org/en/latest/docs/reference/api/geopandas.GeoSeries.contains.html#geopandas.GeoSeries.contains specifies that .contains is exterior-exclusive. That is, the boundary of a Polygon is defined to not be contained within the polygon.

Describe the solution you'd like
In order to implement .contains, I need to verify if our implementations of point-in-polygon follow this same rule. I'll write a test that validates if a point that matches the point of a Polygon is in-polygon. I'll write another test to see if a point that is collinear to two points in the Polygon is in-polygon. If not, great!