Create a module for each value list

[la10736]

Instead to use an anonymous case_1_2_1 we should separate any value list case in a nested submodule named as the identity follow by _<nr>.

An example

#[rstest(a => [1, 2], b => [3, 4]), c, case(5), case(6)]
fn to_test(a:u32, b: u32, c: u32) {
   assert!(a*b != 0);
}```

should generate follow tests:

to_test::case_1::a_1::b_1
to_test::case_1::a_1::b_2
to_test::case_1::a_2::b_1
to_test::case_1::a_2::b_2
to_test::case_2::a_1::b_1
to_test::case_2::a_1::b_2
to_test::case_2::a_2::b_1
to_test::case_2::a_2::b_2

[la10736]

Done