New Result<T> types added

[quicoli]

This PR introduces the following new Result<T>:

• Conflict,
• Created,
• Forbid,
• UnprocessableEntity.

The other changes are only code cleanup actions (removing unused references and code formatting).

[quicoli]

I'd like to continue updating the Extensions project too, but for that we need this change to published first, right?

Thank you for your time reviewing this 👍