feat(receipt, result): easier receipt utils

[hannahhoward]

Goals

Make it easier to work with consuming receipts.

This came up trying to write a client for indexing service -- having to define the whole result schema seems off.

Implementation

Provides a number of simple improvements working with receipts and results:

• simple Unwrap for results
• create receipt reader from success and failure types
• easy way to get back to an actual error from a failure model.

[alanshaw]

Ooh yeah this is really nice 👍