Refactoring: use anyhow for all internal error handling and propagation, but use a final Error for API

[jondot]

Suggestion / Feature Request

The various decompressors use a "central" error enum, which can convert from named and specific error types. Although this is the recommended and acceptable best practice, it makes for an overly verbose coding of an error ergonomics story.

anyhow will chain, wrap, errors, and encourage and allow for adding contexts, which is something we need here.
the only drawback of using anyhow in libraries is that we cannot expose any anyhow type in the public API.

This is why we suggest a refactoring: use anyhow for all internal error handling and propagation, but convert it to a final Error for the public API.

Notes:

• get familiar with anyhow first, see how using context can be cool and nice for "attaching" error information
• convert all Result types to anyhow::Result, this is supposed to be easy
• locate all public API and use an std::Result. this means you need to now convert from anyhow::Result to a standard one. you can use the existing thiserror library to do that