Python tree sitter: Assignment

[titomeister]

As part of porting the PyAST2CAST generation to tree-sitter, we've decided to split the porting to smaller pieces.

This issue involves getting the initial structure of the generation which involves:

• Set up of tree-sitter parser for generating ASTs
• Setup the AST node walker
• Getting a simple end-to-end (Source to GroMEt) generation using a simple assignment program
• Writing tests to make sure the generation is consistent

[titomeister]

Update 9/22:

• Initial setup of tree-sitter has been done
• Initial setup of the AST node walker has been done
• Currently debugging the CAST generation