Rename ScriptHash to Hash160 and add Hash256 to align neow3j with other Neo projects

Other Neo SDKs and devpacks use the UInt160 type to represent script hashes, i.e., hashes produced with RIPEMD, and UInt256 for hashes produced from SHA-256. Neow3j uses the ScriptHash class for UInt160 and does not have any type for UInt256.

We should adapt neow3j to use UInt160 instead of ScriptHash and add UInt256.

Update after discussion (see below): The class ScriptHash will be renamed to Hash160 and a new class Hash256 will be added.

• Rename ScriptHash to Hash160
• Add Hash256

[csmuller]

After an internal discussion we came to the following conclusion.

Using UInt160 and UInt256 is not intuitive to new developers. Hash160 and Hash256 on the other hand are more informative. It becomes clear that the values behind are results of hashing algorithms and that the values are 160 and 256 bits long, respectively. Having specific types like TransactionHash and BlockHash that inherit from Hash256 doesn’t add much value. No other rules would be enforced by such types additionally to the rules enforced by Hash256, i.e. the restriction to 256 bits. We therefore propose to use Hash160 (e.g., for script hashes) and Hash256 (e.g., for block hashes). Hash160 replaces ScriptHash.

This change does not have a high priority but is definitely breaking and needs a bump in the major version number.

[csmuller]

UInt256 is not connected to script hashes in my understanding. Script hashes are hashes of scripts, as the name points out 😉 They are always produces by hasing with sha-256 and then ripmd which produces a 160-bit hash. On the other hand block and transaction hashses, for example, are only hashed with sha-256 and, therefore, produce a 256-bit hash. For them UInt256 is used. Dor the script hashes UInt160 is use.

I think we should rename ScriptHash to UInt160 and add UInt256 as a new type to neow3j using it for example in our io.neow3j.transaction.Transaction class for the getTxId() method.