feat: Add `MapFailure` to `Result`

[seebees]

For :- to work nicely the Failure side of the Result needs to line up with the return value. While this can be simplified by always using the same type, this is an unresonalb requirement.

This lets custsomers align the Failure side of return value. AlignFailure may also be a good name.

Example

  function Foo(): Result<string, int>

  function Bar(): Result<string, string> {
    var fooString :- Foo().MapFailure(_ => "Foo failed.");
    // work
    Success(fooString)
  }

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