Add upgradeable ERC721 SeaDrop proxy tests

[rofergon]

Title: Add upgradeable ERC721 SeaDrop proxy tests

Motivation

The upgradeable package relied on Hardhat/OZ upgrades but shipped without any tests, so the proxy-safe ERC721 implementation had zero coverage. Without parity checks we cannot detect regressions in owner-only forwarding, mint gating, or storage layout across upgrades.

Solution

Added a lightweight SeaDrop mock plus a V2 token stub, then wrote a dedicated Hardhat test suite under src-upgradeable/test/ that deploys the proxy, verifies privileged configuration/minting mirrors the non-upgradeable contract, and asserts state survives upgrades. Wired the upgradeable Hardhat config/tsconfig to compile these specs and documented how to run yarn test:upgradeable. (Tests currently fail here because Node/yarn aren’t installed in this environment.)