Add support for hashing external records

[sportron-ledger]

Checklist

• App update process has been followed
• Target branch is develop
• Application version has been bumped

[codecov-commenter]

Codecov Report

❌ Patch coverage is 98.55072% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 68.44%. Comparing base (f1c47a9) to head (4ba1046).

Files with missing lines	Patch %	Lines
src/account/signature.c	95.65%	1 Missing ⚠️

Additional details and impacted files

@@                  Coverage Diff                   @@
##           dev-smart-contract      #13      +/-   ##
======================================================
+ Coverage               68.00%   68.44%   +0.44%     
======================================================
  Files                      39       39              
  Lines                    4497     4563      +66     
  Branches                  759      761       +2     
======================================================
+ Hits                     3058     3123      +65     
- Misses                   1322     1323       +1     
  Partials                  117      117              

Flag	Coverage Δ
unittests	68.44% <98.55%> (+0.44%)	⬆️

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