Enhance testing

Enhance the testing with property based testing for pack -> unpack scenarios on primitive types, `Value` as well as standard structs (maybe use a macro?). Dependency should be part of `dev-dependencies`. To be decided if these tests are part of the integration test suite. This gives *inner consistency*. Maybe there is more to check with properties?
There are different routes for the standard structs:

- `encode` then `decode` and check that this does not fail and gives the original value
- `encode` and `StdStruct::Foo(foo).encode` which needs to lead to the same bytes
- `Foo::decode` needs to lead to the original value. As well as `StdStruct::decode`.

This applies for primitive types and their `Value` counterpart as well.

Also, enhance the testing to check for the right implementation, i.e. take a few examples and check if they get encoded into the right bytes.