Before 0.30 the Psbt struct implemented Decodable, which can read the correct number of bytes from a Read object. The new deserialize function requires you to know the length of the data you will be decoding (takes &[u8] as argument) and doesn't allow direct reading anymore.

In Fedimint this breaks reading from our DB since we used the Encodable impl to serialize Psbts and never saved the length of that field (fedimint/fedimint#5202). We'll likely end up copying the old Decodable code and doing a DB migration that adds a length field.