MIR: fix big_maps

What

This MR brings the interpretation of the big_maps tzt primitive to MIR.

Why

Improving compatibility MIR and Octez.

Manually testing the MR

When executing cargo run --manifest-path contrib/mir/Cargo.toml --bin tzt_runner tzt_reference_test_suite/*.tzt, one can see that all errors related to big_maps have been solved.