v0.8.3

• feat: support for method in impl trait block as constructor.

  now supports code like the following:

  use rudi::Singleton;
  
  #[derive(Clone)]
  struct One(i32);
  
  #[Singleton]
  impl From<i32> for One {
      #[di]
      fn from(value: i32) -> Self {
          One(value)
      }
  }

• fix: add dev-dependencies for rudi-macro crate.

• chore: simplify the flatten function.

• chore: add assertions to doctests.

• chore: extract functions.