crypto-common: fix SerializableState implementation for [u128; N]

[Eh2406]

Found with AI and Scrutineer. There appears to be a typo that incorrectly records the size of u126. The following test fails before this fix, and passes after it.

#[test]
fn test_serializable_state_u128_array() {
    let array: [u128; 4] = [1; 4];
    let serialized = array.serialize();
    let deserialized = <[u128; 4]>::deserialize(&serialized).unwrap();
    assert_eq!(array, deserialized);
}