stackup.py math error for LEF58_SPACINGTABLE

[ssteffl]

it uses >= instead of >. this will cause min-pitch wires to never be possible. min-width wires should match the "width_at_least": 0.0.

src/hammer-tech/stackup.py line 176 is an example.

I started to fix it, but realized this was an issue in more places than i had realized, so i aborted.

refer to page 479 of lefdef 5.8 spec

[edwardcwang]

@jwright6323

[jwright6323]

Yeah, we talked about this in the meeting on Thursday. I recall deliberately using >=, so I don't think it's a bug but will look into it.