Add Pages and Words libraries for MIP-8 storage pages

[mmv08]

This PR adds two small storage libraries for MIP-8 pages and changes CI to use the upstream Foundry with added monad support.

Contracts added:

• Pages implements the page and slot arithmetic from MIP-8 together with a PageIndex type and PageHandle struct to reserve a storage slot for deriving the page from that slot number.
• Words is a helper to read and write storage without assembly, same approach as OZ's StorageSlot lib

A basic usage sketch:

import {PageHandle} from "monad-std/utils/storage/Pages.sol";

contract Vault {
    PageHandle internal balances;

    function balanceOf(uint256 i) external view returns (uint256) {
        return balances.page().words()[i];
    }

    function set(uint256 i, uint256 v) external {
        balances.page().words()[i] = v;
    }
}

[Copilot]

🟢 Approval recommended

The implementations are internally consistent, bounded appropriately, documented, and covered by focused fuzz tests.

Pull request overview

Adds MIP-8 page arithmetic and typed storage access utilities, with tests, documentation, dependency locking, and upstream Foundry CI support.

Changes:

• Adds Pages, PageIndex, PageHandle, and Words.
• Adds fuzz tests for page arithmetic and storage pointers.
• Updates Foundry configuration, dependencies, CI, and documentation.

File summaries

File	Description
src/utils/storage/Pages.sol	Implements MIP-8 page and slot arithmetic.
src/utils/storage/Words.sol	Adds typed arbitrary-slot storage access.
test/Pages.t.sol	Tests page derivation and arithmetic.
test/Words.t.sol	Tests exact-slot reads and writes.
README.md	Documents the new storage utilities.
foundry.toml	Enables Monad and CI fuzz configuration.
foundry.lock	Locks the forge-std dependency.
.gitmodules	Configures the forge-std submodule.
.github/workflows/test.yml	Uses upstream Foundry and checks out submodules.

Review details

• Files reviewed: 9/10 changed files
• Comments generated: 0
• Review effort level: Balanced

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[Copilot]

🟢 Approval recommended

The storage utilities, tests, dependency setup, documentation, and CI changes are consistent and complete.

Review details

• Files reviewed: 9/10 changed files
• Comments generated: 0 new
• Review effort level: Balanced