fix: handle partial extends in block validation

[brice-stacks]

stacks-inspect validate-block was not correctly handling the partial extends, so it was incorrectly reporting bad block costs.

[aaronb-stacks]

LGTM!

[benjamin-stacks]

This makes maybe 80% sense to me, it seems coherent, and Aaron gave a thumbs up. Good enough 😅

[codecov]

Codecov Report

❌ Patch coverage is 0% with 26 lines in your changes missing coverage. Please review.
✅ Project coverage is 76.25%. Comparing base (267c7ef) to head (e1fff6c).
⚠️ Report is 3 commits behind head on develop.

Files with missing lines	Patch %	Lines
contrib/stacks-inspect/src/lib.rs	0.00%	26 Missing ⚠️

❌ Your project status has failed because the head coverage (76.25%) is below the target coverage (80.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #6786      +/-   ##
===========================================
- Coverage    78.40%   76.25%   -2.16%     
===========================================
  Files          585      585              
  Lines       361384   361397      +13     
===========================================
- Hits        283360   275590    -7770     
- Misses       78024    85807    +7783     

Files with missing lines	Coverage Δ
contrib/stacks-inspect/src/lib.rs	4.98% <0.00%> (-0.08%)	⬇️

... and 97 files with indirect coverage changes

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