fix(core): Return partial response for headers if one fails

[renaynay]

Fixes an issue where we would discard all headers in case one failed. Now we can at least return the ones we synced successfully (as long as they're contiguous from from) so we don't need to do duplicate work.

[codecov-commenter]

Codecov Report

❌ Patch coverage is 80.00000% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 36.00%. Comparing base (2469e7a) to head (4b30d03).
⚠️ Report is 633 commits behind head on main.

Files with missing lines	Patch %	Lines
core/exchange.go	80.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4738      +/-   ##
==========================================
- Coverage   44.83%   36.00%   -8.83%     
==========================================
  Files         265      307      +42     
  Lines       14620    20777    +6157     
==========================================
+ Hits         6555     7481     +926     
- Misses       7313    12326    +5013     
- Partials      752      970     +218     

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