Fix `eval_get` in sierra emu

[FrancoGiachetta]

Currently, in felt252_felt_dict_entry.rs, eval_get is implemented as follows:

pub fn eval_get(
    registry: &ProgramRegistry<CoreType, CoreLibfunc>,
    info: &SignatureAndTypeConcreteLibfunc,
    args: Vec<Value>,
) -> EvalAction {
    let [Value::FeltDict {
        ty,
        mut data,
        mut count,
    }, Value::Felt(key)]: [Value; 2] = args.try_into().unwrap()
    else {
        panic!()
    };
    assert_eq!(info.ty, ty);

    let value = data
        .entry(key)
        .or_insert(Value::default_for_type(registry, &ty))
        .clone();

    count += 1;

    EvalAction::NormalBranch(
        0,
        smallvec![
            Value::FeltDictEntry {
                ty,
                data,
                count,
                key
            },
            value
        ],
    )
}

This is actually wrong with respect to native who, instead of the key, returns a pointer to the entry's value. What this means is that we should be returning this instead:

EvalAction::NormalBranch(
   0,
   smallvec![
       Value::FeltDictEntry {
            ty,
            data,
            count,
            key
        },
        value
    ],
)