Commonize IR Generation and Validation to Rust

[markovejnovic]

Currently, our Python code and our Rust code take separate code paths to generate the IR. The python code emits a JSON IR that the Rust code then consumes.

This has some problems:

• A lot of our tests test that the IR is compatible between Rust and Python. If we had one place of maintenance, we could completely get rid of a huge number of tests.
• There is duplicated logic between Rust and Python.

@Power-el-Tanke has investigated whether it is possible to use pyo3, py-rs.