refactor[next]: new ITIR type inference

[tehrengruber]

New type inference algorithm on ITIR unifying the type system with the one used in the frontend. Types are stored directly in the ITIR nodes. This replaces the constraint based type inference giving significant performance and usability improvements. Types of builtins are expressing using simple to write TypeSynthesizer of the form:

@_register_builtin_type_synthesizer
def power(base: ts.ScalarType, exponent: ts.ScalarType) -> ts.ScalarType:
    return base

[egparedes]

First round of review. I focused mainly in general python aspects and skipped the tests and an in-depth review of the type inference algorithm itself, which I'll do in a following review.

[egparedes]

Just minor comments. I'm still thinking about the idea of transforming the inference algorithm to use a graph instead of callbacks, but it might be out of scope for this PR.

[egparedes]

It looks good. I think it's better to merge the PR now and keep thinking about ways to simplify or improve the inference algorithm in other PRs.

[egparedes]

Don't forget to add a proper PR description before merging.