fix: missing artifacts for ACL, TFHEExecutor, KMSVerifier, GatewayContract contracts

[infinitywarg]

Bug reproduction steps:

• create repository from this template
• cd into the repository
• run 'pnpm install'
• run 'pnpm run fhevm:start'

Error:

Nothing to compile
No need to generate any newer typings.
Nothing to compile
No need to generate any newer typings.
gatewayContractAddress written to gateway/.env.gateway successfully!
node_modules/fhevm/gateway/lib/PredeployAddress.sol file has been generated successfully.
ACL address 0x2Fb4341027eb1d2aD8B5D9708187df8633cAFA92 written successfully!
node_modules/fhevm/lib/ACLAddress.sol file generated successfully!
TFHE Executor address 0x05fD9B5EFE0a996095f42Ed7e77c390810CF660c written successfully!
node_modules/fhevm/lib/FHEVMCoprocessorAddress.sol file generated successfully!
KMS Verifier address 0x12B064FB845C1cc05e9493856a1D637a73e944bE written successfully!
node_modules/fhevm/lib/KMSVerifierAddress.sol file generated successfully!
Error HH700: Artifact for contract "ACL" not found. 

For more info go to https://hardhat.org/HH700 or run Hardhat with --show-stack-traces
Error HH700: Artifact for contract "TFHEExecutor" not found. 

For more info go to https://hardhat.org/HH700 or run Hardhat with --show-stack-traces
Error HH700: Artifact for contract "KMSVerifier" not found. 

For more info go to https://hardhat.org/HH700 or run Hardhat with --show-stack-traces
privateKey 717fd99986df414889fd8b51069d4f90a50af72e542c58ee065f5883779099c6
ownerAddress 0x305F1F471e9baCFF2b3549F9601f9A4BEafc94e1
Error HH700: Artifact for contract "GatewayContract" not found. 

For more info go to https://hardhat.org/HH700 or run Hardhat with --show-stack-traces
 ELIFECYCLE  Command failed with exit code 1.

Root Cause:

• 'npx hardhat clean' in launch-fhevm.sh script removes the entire /artifacts folder
• TFHEExecutor.sol not imported into EncryptedERC20 contract hence artifact is not available in /artifacts/fhevm/lib/ folder

Fix:

• remove 'npx hardhat clean' in launch-fhevm.sh script
• import below contracts into EncryptedERC20 contract

import "fhevm/gateway/GatewayCaller.sol";
import "fhevm/lib/TFHEExecutor.sol";
import "fhevm/lib/TFHE.sol";
import "@openzeppelin/contracts/access/Ownable2Step.sol";

contract EncryptedERC20 is Ownable2Step {
...
...
...