Update hardhat tests to use loadFixture

[grp06]

Describe your changes

• added loadFixture which loads just once compared to beforeEach
• we had this a long time ago but took it out because we wanted to try running tests on a live network at some point, which wasn't necessary
• tests now run in 8s instead of 18s

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• I have updated the documentation accordingly. (if applicable)
• All new and existing tests passed.

[linear]

DEV-786 re-implement loadFixture in hardhat tests

1. const { loadFixture } = require("nomicfoundation/hardhat-network-helpers");
2. we only got rid of loadFixture as an experiment when we first pushed our contracts to Goerli in order to run our tests on a live network... Re-implementing it will speed up our hardhat tests considerably