Add tests for the `conversions` crate

[Radinyn]

• assert x.to_y().to_x() == x
• create new objects from 1

[devnet0x]

GM @Radinyn ...Would you be okay with something like this?

#[test]
fn test_class_hash_conversions() {
    let felt: StarkFelt = StarkFelt::new([1u8; 32]).unwrap();
    let class_hash = ClassHash(felt);

    assert_eq!(class_hash,class_hash.to_felt252().to_class_hash());
    assert_eq!(class_hash,class_hash.to_field_element().to_class_hash());
    assert_eq!(class_hash,class_hash.to_stark_felt().to_class_hash());
    assert_eq!(class_hash,class_hash.to_stark_hash().to_class_hash());
    assert_eq!(class_hash,class_hash.to_contract_address().to_class_hash());
    assert_eq!(class_hash,class_hash.to_short_string().to_class_hash());
    assert_eq!(class_hash,class_hash.to_nonce().to_class_hash());
}

[devnet0x]

gm..may i be assigned to this issue?..thanks

[devnet0x]

src/stark_hash.rs conversion is missing, may i add it @cptartur ?

[Arcticae]

@devnet0x what you proposed above looks fine to me, although i would add more values to the test itself.

as for stark_hash.rs test - i think you can add it

[devnet0x]

I think its done...please could you check?...thanks