dynamic Python dialect

[Roger-luo]

create a dyanmic python dialect in rust which also serve as a PyO3 PyObject so one can create and manipulate the dialect definition from Python. Below is a rough sketch of what this could look like

struct PyStatement {
    arguments: Vec<SSAValue>,
    blocks: Vec<Block>,
    digraphs: Vec<DiGraph>,
    ungraphs: Vec<UnGraph>,
    successors: Vec<Successor>,
}

#[pyobject]
struct PyDialect {
    statements: Vec<PyStatement>,
}