Consider using decode_all for get_contract_storage

[ascjones]

Raised by @DamianStraszak.

At the moment get_contract_storage uses scale::Decode::decode, which can succeed even if not all bytes are consumed. This would be an issue where corrupted or invalid bytes in a storage cell are successfully decoded, but the expectation is that this should fail.

We should investigate using decode_all instead which will fail if there are bytes remaining in the input after decoding successfully.

Note that this may technically be a "breaking" change if existing contracts are (ab)using this behaviour, so will require some communication if we go ahead with it.