Add StorageSlot library and ERC1967 upgradeable proxy contracts

[Copilot]

Adds the standard OpenZeppelin-style upgradeable proxy stack (originally submitted for verification at polygonscan.com on 2021-06-12) as contracts/TransparentUpgradeableProxy.sol.

Contracts added

• StorageSlot — read/write address, bool, bytes32, uint256 at arbitrary EVM storage slots via inline assembly, avoiding storage layout collisions in upgradeable contracts
• Address — low-level call helpers (isContract, sendValue, functionCall, functionDelegateCall, etc.)
• IBeacon — interface for beacon proxy targets
• ERC1967Upgrade — EIP-1967 compliant slot management for implementation, admin, and beacon addresses; includes rollback-safe _upgradeToAndCallSecure
• Proxy — delegatecall-based fallback base
• ERC1967Proxy — proxy backed by EIP-1967 implementation slot
• TransparentUpgradeableProxy — admin-gated upgrade functions using the transparent proxy pattern to prevent selector clashing

Usage example

// Read/write a value at a known EIP-1967 slot
bytes32 slot = 0x360894...;
StorageSlot.getAddressSlot(slot).value = newImplementation;
address impl = StorageSlot.getAddressSlot(slot).value;

---

💬 We'd love your input! Share your thoughts on Copilot coding agent in our 2 minute survey.