[hc-spin-rust-utils] Remove `.unwrap()`s and add proper error handling

There are a bunch of `.unwrap()`s in the code that should get replaced with proper error handling. [This PR](https://github.com/lightningrodlabs/we-rust-utils/pull/6/files) may be taken as guidance on how to do that.

Start by locating the `.unwrap()` call sites in the repository and review the linked PR for the project's error-handling approach. Done means the identified unwraps have been replaced with proper error handling without leaving the issue's targeted cases unresolved.

Written by the indexing model from the issue text.