implicit hash map

[ModProg]

Implicit maps should probably work for HashMaps.

Testcase for src/tests/serde.rs:

#[test]
fn implicit_hash_map() {
    roundtrip_implicit_map(
        &HashMap::from([(String::from("Hello"), 1), (String::from("World"), 2)]),
        "\"Hello\": 1\n\"World\": 2",
    );
}