api, tests: streamline invoke return types

[ixje]

Currently all test_* functions of ChainFacade directly return the actual result of the called method on the smart contract. Which is very convenient when only using test invokes, but makes it inconvenient when switching between invoke_ and test_invoke because now the return type changed.

Personally when writing code that ends up persisting to chain (via invoke) I start off with test_invoke (also with debugging) before swapping it over. By streamlining the return types one does not have to change the result handling code.

Changes in this PR

• all test_invoke* now return an InvokeReceipt just like regular invoke* calls
• invoke_multi and invoke_multi_raw return InvokeReceipt[Sequence] instead of Sequence