[SC-1140] Export bySig js helpers to package

[zZoMROT]

Static Code Analysis (readability, compactness):

Hasn't changed

Dynamic Code Analysis (external APIs, interaction flows):

Methods have become available for convenient data preparation for the bySig contract

Efficiency (gas costs, computational complexity, memory requirements):

Hasn't changed

Opinion, trade-offs and other thoughts (optional):

Seems useful, should add

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.33%. Comparing base (176d078) to head (f0c2566).

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #145   +/-   ##
=======================================
  Coverage   93.33%   93.33%           
=======================================
  Files          17       17           
  Lines         345      345           
  Branches       67       67           
=======================================
  Hits          322      322           
  Misses         23       23           

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