Implementations - Biguint - Rust + Mx

[virgil-serbanuta]

Needed for #34

• Translating BigUint-BigUint arithmetic operators (+, -, *, /) to hook calls
• Translating BigUint-BigUint relational operators (<, <=, >, >=, ==, !=) to hook calls. We may want to rewrite the Rust code to use only <, <= and ==.
• Translating BigUint-u64 operators to hooks (most likely we only need *)
• BigUint::zero() to hook
• BigUint::from(_) to hook