Bound sync loops in lightning-transaction-sync

[TheBlueMatt]

If we start syncing from an electrum or esplora server and find that the chain moved during our sync, we reset and start fresh. However, if that happens repeatedly, we probably shouldn't just spin forever. Here we give up after ten attempts and just hope we can sync properly later.

[ldk-reviews-bot]

👋 Thanks for assigning @tnull as a reviewer!
I'll wait for their review and will help manage the review process.
Once they submit their review, I'll check if a second reviewer would be helpful.

[ldk-claude-review-bot]

No new issues found. All previously identified problems have been resolved in the current version of the diff:

1. The compile error (_ vs i in electrum.rs) is fixed.
2. The fallthrough to the "Finished" log on give-up is fixed — both files now use return Err(TxSyncError::Failed).

The only remaining observation (dead upper bound of 100 when 10 is the effective limit) was already posted in a prior review pass.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.43%. Comparing base (44828f7) to head (1c7fcb7).
⚠️ Report is 17 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4612      +/-   ##
==========================================
+ Coverage   86.12%   86.43%   +0.30%     
==========================================
  Files         157      158       +1     
  Lines      108922   109293     +371     
  Branches   108922   109293     +371     
==========================================
+ Hits        93812    94463     +651     
+ Misses      12495    12284     -211     
+ Partials     2615     2546      -69     

Flag	Coverage Δ
fuzzing-fake-hashes	5.08% <ø> (?)
fuzzing-real-hashes	22.78% <ø> (?)
tests	86.16% <ø> (+0.03%)	⬆️

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