Duplication

[ozgunozerk]

This pr:

• fixes the double invocation problem:
  • previously: when this macro is invoked on more than 1 struct in the same module/file, it creates the same sealed traits and structs, which causing compile error
  • this is fixed by adding the name of the struct as a prefix to these common structs & traits
• adds support to retain the full signature of the methods (async, const, generics, etc.)
  • previously we were only retaining the lifetimes and generics for the struct
• adds support to enable wrapping the struct in complex types like Result<Option<Struct>> for the methods
  • in both return type
  • and in the body

Fixes #16 and #17