R4R: Round down when calculating rewards (fixes F1 sim bug)

[cwgoes]

Closes #3354

Always round down when calculating rewards in F1 fee distribution. As far as I can tell, this fixes all the F1-related simulation issues, but I haven't yet run a long multi-seed test.

• Linked to github-issue with discussion and accepted design OR link to spec that describes this work.
• Wrote tests
• Updated relevant documentation (docs/)
• Added entries in PENDING.md with issue #
• rereviewed Files changed in the github PR explorer

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For Admin Use:

• Added appropriate labels to PR (ex. wip, ready-for-review, docs)
• Reviewers Assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[codecov]

Codecov Report

Merging #3359 into jack/makefile-fix will decrease coverage by 0.02%.
The diff coverage is n/a.

@@                 Coverage Diff                  @@
##           jack/makefile-fix   #3359      +/-   ##
====================================================
- Coverage              54.93%   54.9%   -0.03%     
====================================================
  Files                    132     132              
  Lines                   9645    9645              
====================================================
- Hits                    5298    5296       -2     
- Misses                  4014    4016       +2     
  Partials                 333     333