[tech debt] migrate testing from era-test-node to anvil-zksync #135
Description
era-test-node is very outdated and no longer supported. anvil-zksync should be used instead.
The issue is that hardhat's chai matchers that we currently use for testing make a lot of assumptions that don't hold for anvil-zksync -- in particular, the behavior around rejected transactions is different, hence, matchers have to be patched.
Once the test infra is migrated, we can also consider re-enabling the e2e demo-app test which was disabled in #91