[openzeppelin-contracts fork] Add hardhat-solx plugin config for solx benchmark

[marianfe]

Summary

• Add @nomicfoundation/hardhat-solx plugin to enable solx compilation via --build-profile test
• Update default compiler version from 0.8.31 to 0.8.33 (required for solx 0.1.3)
• Suppress solx memory-unsafe assembly warning (code 5726)

Usage

# Compile with solc (default profile)
npx hardhat compile

# Compile with solx (test profile, auto-created by plugin)
npx hardhat compile --build-profile test

Notes

• Depends on unreleased packages: hardhat@^3.2.0 and @nomicfoundation/hardhat-solx@^3.0.0
  PRs on hardhat main:
  Improve multi-compiler support in the build system by adding a SolidityCompilerConfig base interface NomicFoundation/hardhat#8008
  Add downloadCompilers parallel hook for extensible compiler downloads NomicFoundation/hardhat#8009
  Add @nomicfoundation/hardhat-solx plugin NomicFoundation/hardhat#8034
• Based on the Hardhat 3 migration from Amxx/openzeppelin-contracts@hardhat3