refactor: handle errors instead of panicking with unwrap in non-test code

[notheotherben]

Summary

Removes every .unwrap() from non-test code, replacing each with proper error handling so failures surface as human-readable errors instead of panics. The remaining .unwrap() calls are all inside #[cfg(test)] modules.

Changes

• src/sources/github_repo.rs & src/sources/github_gist.rs: Moved the fallible from and recovery parsing inside the try_stream! block so parse errors propagate through the Result stream via ? instead of unwrapping. The recovery-mode parse now uses a match that returns the default when unset and yields the parse error otherwise.
• src/sources/github_releases.rs: Moved the target parse into the stream! block (yielding the error and returning on failure), and replaced two if let Err(...) { … } … .unwrap() patterns with match expressions.
• src/pairing.rs: Replaced join_next().await.unwrap().unwrap() and fut.unwrap() with match arms that yield task results and convert a tokio::task::JoinError (from a panicked/cancelled backup task) into a human_errors::Error.
• src/errors.rs: Added a HumanizableError implementation for tokio::task::JoinError, following the existing pattern.

Testing

• cargo check --all-targets passes.
• cargo test passes for all 151 tests, except one pre-existing live-network integration test (get_releases::case_1) that hit a GitHub API rate limit (403). Notably, the refactor correctly propagated that 403 as a proper error through the stream rather than panicking internally.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 12 lines in your changes missing coverage. Please review.
✅ Project coverage is 74.43%. Comparing base (90c5373) to head (f3a497b).
⚠️ Report is 3 commits behind head on main.

Files with missing lines	Patch %	Lines
src/errors.rs	0.00%	7 Missing ⚠️
src/main.rs	0.00%	3 Missing ⚠️
src/sources/github_gist.rs	0.00%	1 Missing ⚠️
src/sources/github_repo.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #619      +/-   ##
==========================================
- Coverage   75.35%   74.43%   -0.93%     
==========================================
  Files          31       31              
  Lines        2447     2394      -53     
==========================================
- Hits         1844     1782      -62     
- Misses        603      612       +9     

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