Consider adding LazyIO and friends

The thing about `IO` in multiple languages / libraries is that it is lazy.

Our `IO` is not lazy by design. It is done, so Python developers can use it like so: `impure(print)(1) # prints "1"`
But, we also need to think about other problems as well:
1. Retries, with proper lazy `IO` one can retry an operation as many times as one wishes: `p = impure_lazy(print)(1); p(); p() # prints "1" twice`
2. Semantical identity to `Future`, currently it is not similar to regular `IO`, because `Future`s are lazy: they don't run until they are executed properly
3. New users will find the similar data-type they already know from other languages / libraries

まず、既存の IO と Future の実装および impure API を読みます。issue では特定のファイルは指定されていません。それらの評価動作を比較し、retry のセマンティクスと Future との相互作用を含む、意図する LazyIO API を定義します。遅延実行と繰り返しの呼び出しを実証する、合意済みの設計とテストがあれば完了です。

索引モデルが issue の本文から書いたものです。