feat(schema)!: prepend module to declarations in BorshSchema

[dj8yfo]

this pr is copy of #300
sketch of possible solution to #92, both the original issue and the widened perspective

this results in

    #[derive(borsh::BorshSchema)]
    enum A {
        Bacon(Vec<i64>),
        Eggs,
    }

=>

{
    "Vec<i64>": Sequence {
        length_width: 4,
        length_range: 0..=4294967295,
        elements: "i64",
    },
    "i64": Primitive(
        8,
    ),
    "tests::schema::test_simple_enums::A": Enum {
        tag_width: 1,
        variants: [
            (
                0,
                "Bacon",
                "tests::schema::test_simple_enums::___ABacon",
            ),
            (
                1,
                "Eggs",
                "tests::schema::test_simple_enums::___AEggs",
            ),
        ],
    },
    "tests::schema::test_simple_enums::___ABacon": Struct {
        fields: UnnamedFields(
            [
                "Vec<i64>",
            ],
        ),
    },
    "tests::schema::test_simple_enums::___AEggs": Struct {
        fields: Empty,
    },
}

---

this may have very weak interoperability with borsh-js due to being specific to rust