Statistics module in pytato

Although there is already a stats module in loopy, I'm working towards a vanilla stats module in pytato.

Q. Why not just use `loopy.get_op_map`?
A. For the kernels I'm looking at generating loopy takes around 1.5 minutes and the stats module in loopy needs to preprocess the translation unit which is yet another 4 minutes.

Please let me know if there are serious drawbacks to this approach.

Start by reading loopy.get_op_map and the existing loopy stats module, then inspect pytato's kernel-generation entry points to understand where a vanilla statistics module could fit. The issue does not name any pytato files or tests; done would require an agreed scope and API rather than an implementation target.

Written by the indexing model from the issue text.