feat: add faucet client support

[init4samwise]

Summary

Add faucet functionality to the TypeScript SDK for requesting testnet tokens programmatically.

Features

• createFaucetClient() factory function for creating faucet clients
• requestTokens(address, assets?) to request USD and/or ETH testnet tokens
• checkCooldown(addresses) to check rate limit status for up to 100 addresses
• canRequest(address) convenience method to check if an address can request tokens
• Comprehensive error handling with typed FaucetRequestError
• Full TypeScript types for all API requests and responses

Usage

import { createFaucetClient } from "@signet-sh/sdk/faucet";

const faucet = createFaucetClient("https://faucet.pecorino.signet.sh");

// Request testnet tokens
const result = await faucet.requestTokens("0x...");
console.log(result.message);

// Check if can request more
const canDrip = await faucet.canRequest("0x...");

Testing

• 15 unit tests covering all functionality
• Mocked fetch for isolated testing
• Tests for success, error, and edge cases

Closes ENG-1838