fix: surface electrum error when server returns invalid genesis hash

[reez]

Description

Propagates invalid genesis hashes instead of panicking.

Notes to the reviewers

Changelog notice

Checklists

All Submissions:

• I've signed all my commits
• I followed the contribution guidelines
• I ran cargo fmt and cargo clippy before committing

New Features:

• I've added tests for the new feature
• I've added docs for the new feature

Bugfixes:

• This pull request breaks the existing API
• I've added tests to reproduce the issue which are now passing
• I'm linking the issue being fixed by this PR

[reez]

upstream electrum never trys to construct a BlockHash (stops at deserializing into raw bytes) like we are trying to do here in bdk-ffi, so I'm proposing this extra check here (and not panic) in the case the parse fails, while uncommon for electrum to pass something bad back to us we should treat this sort of failure as a recoverable error (surfacing the error) instead of crashing.

I can add a test, but hopefully the above comment makes sense, feel free to ask me anything else related to this though.

just rebased PR now, fyi is all @thunderbiscuit

[rustaceanrob]

Although it will probably never happen, good to protect against a malicious server

ACK 2578420

[thunderbiscuit]

ACK 2578420. Just needs a rebase.

[reez]

rebased