fix: harden the order of keys that needs to be serialized

[eliax1996]

Why this way

Previously we were relying on the fact that the .keys() order and the json.dumps() order are always sync. This enforces by the OrderedDict a fixed order. Not sure if the same odering check should be performed also for the is_key_in_canonical_format, probably here we want to ensure that the current dict has exactly the same order in the keys().

[eliax1996]

Need to do the same for the canonical format