optimized ast

[s-cork]

Before running the symtable in compile.c there is an ast optimization phase that we should explore.

It seems to do some code folding of literal values.

see ast_opt.c

[s-cork]

python/cpython#2858
Problems with the c approach - they change the nodes inplace.
We can't really do that.
I mean we could - but it would be horrible

tests

I couldn't find any in python 🤷‍♂️ but this discussion about the above PR points to these tests
https://github.com/vstinner/fatoptimizer/blob/master/test_fatoptimizer.py

pypy has an interesting approach that allows for inplace mutation.
I think we should try this approach
https://github.com/mozillazg/pypy/blob/master/pypy/interpreter/astcompiler/optimize.py
https://github.com/mozillazg/pypy/blob/522cfbedda554843fd989f1b1214e61b47fce0ab/pypy/interpreter/astcompiler/ast.py

That approach might also be nice for other places we do walk the node tree