Further Optimize Bounds Counstriction

[philipc2]

Taken from #1180 (comment)

Timings were taken on a single NCAR Derecho CPU node.

Resolution	Nodes	Faces	Edges	Grid Load Time (s)	Bounds Construction Time (s)	Total Time (s)
30km	1,310,720	655,362	1,966,080	1.923	2.541	4.464
15km	5,242,880	2,621,442	7,864,320	7.489	10.191	17.68
7.5km	20,971,520	10,485,762	31,457,280	29.228	37.866	67.095
3.75km	83,886,080	41,943,042	125,829,120	113.028	155.486	268.514