Installing external packages
Approach #1
Using forge install
Openzepplin
Ref https://docs.openzeppelin.com/contracts/5.x/
forge install OpenZeppelin/openzeppelin-contracts
Update/add remappings.txt
@openzeppelin/contracts/=lib/openzeppelin-contracts/contracts/
Approach #2
Using npm
npm install @openzeppelin/contracts
Update/add remappings.txt
@openzeppelin/contracts/=node_modules/@openzeppelin/contracts