[Rust] Support row map

[theweipeng]

What do these changes do?

1. Ensure that the library only exports the necessary modules.
2. Rust row format support Map.
   Add a new binary accessor named MapGetter, which wraps two ArrayGetter instances to access keys and values. Additionally, include a function to convert keys and values into a BTreeMap.

usage:

#[test]
fn rowmap() {
    #[derive(FuryRow)]
    struct Foo {
        f5: BTreeMap<String, String>,
    }

    let mut f5: BTreeMap<String, String> = BTreeMap::new();
    f5.insert(String::from("k1"), String::from("v1"));
    f5.insert(String::from("k2"), String::from("v2"));

    let row = to_row(&Foo {
        f5,
    },);

    let obj = from_row::<Foo>(&row);
    let binding = obj.f5();

    assert_eq!(binding.keys().size(), 2);
    assert_eq!(binding.keys().get(0), "k1");

    assert_eq!(binding.values().size(), 2);
    assert_eq!(binding.values().get(0), "v1");

    let f5 = binding.to_btree_map().expect("should be map");
    assert_eq!(f5.get("k1").expect("should exists"), &"v1");
    assert_eq!(f5.get("k2").expect("should exists"), &"v2");
}

Related issue number

Closes #1205

Check code requirements

• tests added / passed (if needed)
• Ensure all linting tests pass, see here for how to run them

[chaokunyang]

LGTM, great work!