Should we keep (`Module`, `Bundle`, `Sim`, etc) non-schema attributes around?

[dan-fritchman]

Example:

@h.module 
class M:
  n = 5 
  i = h.Input(width=n)

M.n # <= the issue

The issue: is M.n

• A thing (probably 5), or
• An AttributeError

Current answer is the latter