Rewrite control flow inside loops.
Closes #393.
Loops are already translated as folds. This PR wraps their accumulators to add control flow information (in case of break return or continue). Some specific fold operators are also added to handle these wrapped accumulators.
Code generation should be almost stable. The remaining part is to write the specific folds as part of the fstar Rust_primitives
@W95Psp still testing but you can start to review.
@W95Psp I think I fixed everything according to your feedback!
Great, looking at it. Next PR can you resolve discussions that you think are handled?