Make Via creation happen immediately upon calling self.add_via()

[pvnbhargava]

The Problem

Currently, self.add_via() creates a Via object which calculates the region to be filled with vias and can be mutated in real time. However, This Via object does not actually try to fill this region until the generator gets finalized.

As a result, any exceptions that may result from of incorrect metal sizing does not show up until the generator finishes, and can not easily be attributed to the line of code which created the via in the first place

Proposed Solution

As soon as self.add_via() is called, we should call the tech class' get_best_via_info() method to determine optimal via sizing for the provided region. This way, if a via is not possible, it will fail immediately. Once this optimal via info is calculated, we can construct a primitive via object with it.