Use Hardhat client and ethers in unit tests

[cgewecke]

• Replaces ganache client with a Hardhat provider in unit tests
• Replaces truffle-contract with ethers in unit tests
• Removes truffle/contract depedency

In tests that revert, the hit counts have had to be adjusted downwards because truffle-contract re-executed the transaction as a call to fetch the revert reason.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (c3c5615) 95.85% compared to head (35f0d20) 95.85%.

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Additional details and impacted files

@@           Coverage Diff           @@
##           master     #847   +/-   ##
=======================================
  Coverage   95.85%   95.85%           
=======================================
  Files          19       19           
  Lines        1061     1061           
=======================================
  Hits         1017     1017           
  Misses         44       44           

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