Tuple passthrough should be toggleable

[Joseph Perez]

apischema doesn't allow to deserialize tuple by default. However, it can be an issue for example with the idiom deserialize(MyType, serialize(MyType, my_obj)) if MyType contains some tuples of primitives (see pcdshub/whatrecord#110). User could also expect the serialized data to contains only lists, for instance to write test assertions.

As other passthrough optimization, I think it should be deactivated by default