improve(package): Script target for clean

Also, having typechain output is a pre-requisite for the `build` target,
so add a hook for typechain to run if the typechain dir does not exist.

package.json

@@ -18,12 +18,13 @@
   "types": "dist/index.d.ts",
   "main": "dist/index.js",
   "scripts": {
+    "clean": "for dir in dist node_modules typechain; do mv \"${dir}\" \"_${dir}\" 2>/dev/null; rm -rf \"_${dir}\" & done",
     "compile-zksync": "COMPILE_ZK=true yarn hardhat compile",
     "lint-contracts": "yarn solhint ./contracts/**/*.sol",
     "lint": "yarn prettier --list-different",
     "lint-fix": "yarn prettier --write",
     "prettier": "prettier .",
-    "build": "hardhat compile && tsc && rsync -a --include '*/' --include '*.d.ts' --exclude '*' ./typechain ./dist/",
+    "build": "[ -d typechain ] || yarn generate-contract-types && hardhat compile && tsc && rsync -a --include '*/' --include '*.d.ts' --exclude '*' ./typechain ./dist/",
     "test": "hardhat test",
     "test:report-gas": "REPORT_GAS=true hardhat test",
     "test:gas-analytics": "GAS_TEST_ENABLED=true hardhat test ./test/gas-analytics/*",