Helper function to parse the return value

[DOBEN]

Invoking a smart contract via the Rust SDK returns the raw bytes. Developers need to handle the conversion from bytes to the desired Rust type for now.
https://github.com/Concordium/concordium-rust-sdk/blob/main/src/types/smart_contracts.rs#L234

In the testing library, we provide a helper function to deserialize the return value into a given Rust type.
https://github.com/Concordium/concordium-rust-smart-contracts/blob/main/contract-testing/src/types.rs#L651

A similar helper function would be useful in the SDK. Implementation the Read trait on the ReturnValue type could potentially already achieve a basic, yet rather difficult-to-discover way of parsing the bytes (https://doc.rust-lang.org/nightly/std/io/trait.Read.html).

A parse() or try_into() function (easier to discover) can then make use of the Read trait.

let return_value = invoke( .... );
let custom_type:CustomType = return_value.parse().unwrap();

or

let return_value = invoke( .... );
let custom_type:CustomType = return_value.try_into().unwrap();