Add extendConfig logic for hardhat-viem plugin

[cgewecke]

#874, #819

PR adds logic to support the hardhat-viem plugin. If you run the env variable set as below it will configure the hardhat network correctly in the extendConfig hook and skip provider redefinition at the task level.

SOLIDITY_COVERAGE=true npx hardhat coverage

This approach is necessary because there's no way to know from within extendConfig whether the coverage task is actually being run and therefore no safe way to redefine the network settings.

If viem is defined in the hardhat environment and the network has not been set with the correct defaults, an error is thrown:

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.61%. Comparing base (011ee40) to head (ac4a0b3).

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #883      +/-   ##
==========================================
+ Coverage   96.45%   96.61%   +0.15%     
==========================================
  Files          19       19              
  Lines        1045     1062      +17     
==========================================
+ Hits         1008     1026      +18     
+ Misses         37       36       -1     

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