fix: do not panic when parsing invalid hashes (#68)

## Description

Same issue as n0-computer/iroh#3155

## Breaking Changes

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including how to migrate older code. -->

## Notes & open questions

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## Change checklist

- [ ] Self-review.
- [ ] Documentation updates following the [style
guide](https://rust-lang.github.io/rfcs/1574-more-api-documentation-conventions.html#appendix-a-full-conventions-text),
if relevant.
- [ ] Tests if relevant.
- [ ] All breaking changes documented.

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Co-authored-by: Ruediger Klaehn <[email protected]>

Author: dignifiedquire