Use message id as a identifier for duplication check mechanism

[skibitsky]

Currently, the client JSON RPC duplication mechanism uses the client JSON RPC ID as a unique identifier to detect duplicated client JSON RPC requests.

Since this approach doesn't guarantee the uniqueness of IDs and there's a chance of conflicts a new approach with higher entropy is introduced.

The new id is a sha256 function of the decrypted payload of the client request:
message_id = sha256(decrypted_payload)

Testing:

• Make sure that backward compatibility is not broken
• Cross-platform testing (js, swift, kotlin, flutter)

Here is where the id is currently generated in WalletConnectSharp:

• TypeMessageHandler.SendRequest
• JsonRpcRequest constructor (if id is null)
• RpcPayloadId.Generate (can be replaced with new logic)

You could pass a new calculated id to the JsonRpcRequest constructor in the TypeMessageHandler.SendRequest function, which would make the change backwards compatible.

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Original issue in WalletConnectUnity: #103