Warn if rounding affects close coords

[shyamamrith]

If two (or more) coordinates are "close" to one another in the chosen CRS, they can end up occupying the same point after rounding. The errors which arise as a result are not indicative of the problem and so would be hard for a user to debug. Ideally implement a warning to the user if this is the case.

• Check if there is any Shapely routine (or otherwise) to detect whether the points in a polygon will be "merged" as a result of a given rounding precision