Unit test review: Dynamic block rewards

[Incede]

What was the problem?

This PR resolves #8025

How was it solved?

• / with BigInt is equivalent to // in LIP hence no change required
• updated terminology and added comment to indicate formulation of BigInt(5)
• moved specified tests to beforeTransactionsExecute
• no change required for setting context
• added unit test "Should not store timestamp when it is not end of round"
• other 2 tests suggested are not in the scope of unit test for this particular module

How was it tested?

Updated unit tests pass

[codecov]

Codecov Report

Merging #9104 (8e1c5a0) into release/6.1.0 (36a1df9) will decrease coverage by 0.01%.
The diff coverage is n/a.

❗ Current head 8e1c5a0 differs from pull request most recent head 8db170d. Consider uploading reports for the commit 8db170d to get more accurate results

@@                Coverage Diff                @@
##           release/6.1.0    #9104      +/-   ##
=================================================
- Coverage          84.35%   84.34%   -0.01%     
=================================================
  Files                652      652              
  Lines              23970    23966       -4     
  Branches            3490     3489       -1     
=================================================
- Hits               20219    20215       -4     
  Misses              3751     3751              

see 2 files with indirect coverage changes

[vjaiman]

Looks good.