Fix Issues with Makefile in circom-circuit Directory

[susumutomita]

Description

This update in the myna-wallet-monorepo/packages/circom-circuit package's Makefile addresses specific issues related to directory creation and file paths. The changes enhance the overall functionality and ensure the correct setup for circuit compilation and verification.

Key Changes

1. Directory Creation Command Improvement: Updated the init target from mkdir ./setup && mkdir ./build to mkdir -p ./setup && mkdir -p ./build. This change prevents errors if directories already exist.

2. Updating Powers of Tau File Download URL: Changed the curl command from downloading powersOfTau28_hez_final_19.ptau to powersOfTau28_hez_final_20.ptau, ensuring the script uses the latest version of the file.

3. . Correct File Paths for Powers of Tau Files: Adjusted file paths in gov-sig-build-circuit and user-sig-build-circuit targets.

Related Issue

#50