Make internal blockchain methods private

[Exca-DK]

Closes #2257

This PR unexports private blockchain functions that rely on transactions by copying the required functions to the migration package.

[codecov]

Codecov Report

Attention: Patch coverage is 66.89655% with 48 lines in your changes missing coverage. Please review.

Project coverage is 74.53%. Comparing base (0c6508c) to head (e141ac0).
Report is 4 commits behind head on main.

Files with missing lines	Patch %	Lines
migration/blockchain.go	61.73%	29 Missing and 15 partials ⚠️
blockchain/blockchain.go	85.00%	0 Missing and 3 partials ⚠️
migration/migration.go	88.88%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2386      +/-   ##
==========================================
- Coverage   74.69%   74.53%   -0.16%     
==========================================
  Files         110      111       +1     
  Lines       12109    12222     +113     
==========================================
+ Hits         9045     9110      +65     
- Misses       2366     2398      +32     
- Partials      698      714      +16     

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