Align function result analysis more closely with wit

[mschuwalow]

https://github.com/golemcloud/golem/blob/main/golem-worker-executor-base/src/function_result_interpreter.rs#L49

Currently the analysis either returns a tuple (which is always single element in practice) or a record. According to wit docs it will either be a single value or a named list of results.
Goal of this ticket is to simplify the analysis and get rid of the tuple wrapping in the simple value case.