fix: replace relative import paths with remapping paths

[pyropy]

Replaces relative import paths with forge remapping paths.

Using relative paths causes issues when trying to verify contract source code using @fil-b/filfox-verifier:

 npx @fil-b/filfox-verifier forge 0x5991E4F9fcEF4AE23959eE03638B4688A7e1EcfF src/FilBeamOperator.sol:FilBeamOperator --chain 314159     
  

⠹ Verifying contract on Filfox...

Verification Result:
✖ ⚠️  Compilation error in source files.
✖ 📝 Details: ParserError: Source "lib/openzeppelin-contracts-upgradeable/contracts/proxy/utils/Initializable.sol" not found: File import callback not supported
 --> @pdp/PDPVerifier.sol:9:1:
  |
9 | import {Initializable} from "../lib/openzeppelin-contracts-upgradeable/contracts/proxy/utils/Initializable.sol";
  | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^