Remove dependency on Hardhat

[frangio]

Because Hardhat v3 is async ESM it cannot be required. This removes that dependency by adding a flag --paths that should be used to compute the paths before invoking the transpiler. Note that paths also have to be adjusted to v2 shape at the moment, e.g.:

paths="$(node <<'EOF'
  import { config } from "hardhat";
  const { paths } = config;
  paths.sources = paths.sources.solidity[0];
  console.log(JSON.stringify(paths))
EOF
)"

npx @openzeppelin/upgrade-safe-transpiler --paths "$paths" ...