ram: add placement sanity checks to the regression tests (`check_placement`, etc.)

[rovinski]

The ram tests don't feature any basic sanity tests to ensure that the result is correct. Sometimes visual inspection isn't sufficient.

• Tests should add check_placement after running in order to ensure that cells were not placed on top of each other or are otherwise overlapping
• The power grid should be checked to ensure that there are no unconnected pins
• I think that routing violations are already checked, so that's ok
• Formal equivalence should be checked, but that can be a separate issue
• Any other built-in checks that can be run

[rovinski]

@tnguy19