Update Integer Square Root Function

[chgorman]

Scope

Update Integer Square Root function and add additional tests for gas consumption.

Why?

This version of integer square root function has proof of convergence;
it also reduces gas from an average of 1283 to 1259 per call.

[codecov]

Codecov Report

Merging #117 (dbb216c) into main (464a465) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #117      +/-   ##
==========================================
+ Coverage   53.23%   53.25%   +0.01%     
==========================================
  Files         337      337              
  Lines       42984    42991       +7     
  Branches      360      362       +2     
==========================================
+ Hits        22883    22895      +12     
+ Misses      17671    17670       -1     
+ Partials     2430     2426       -4     

Impacted Files	Coverage Δ
bridge/contracts/libraries/math/Sigmoid.sol	100.00% <100.00%> (ø)
badgerTrie/smt_merkle_proof.go	69.53% <0.00%> (+3.90%)	⬆️

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[vtleonardo]

This is awesome @chgorman ! Overall the PR LGTM, just fix the formatting issues on the new contract. You can do it by running:

cd bridge
npm run format

If you don't like the output of the linter on this file, just put it to be ignored in the ./bridge/.solhintignore

[chgorman]

I ran the linter. I do think the previous version is better as it is a bit easier to understand in some parts (like the bit length computation), but that is fine.