feat: add response caching to wallet integration

[0xjerah]

Summary

• Adds a WalletCache class (src/utils/web3/walletCache.ts) with generic TTL-based in-memory caching and prefix-based invalidation
• Caches NFT gallery responses for 5 minutes, DeFi staking positions for 60 seconds, and native balance for 30 seconds
• Cache is automatically invalidated on wallet disconnect, and kept in sync after stake/unstake mutations
• Adds fetchBalance to useWeb3Wallet — fetches native ETH/MATIC balance via eth_getBalance and caches the result
• Extends queryKeys.ts with wallet-specific key factories (balance, nfts, positions, transactions)
• Exports all cache primitives (WalletCache, walletCache, walletCacheKeys, CACHE_TTL) from @/utils/web3

Test plan

• 23 unit tests for WalletCache covering get/set/has/delete/clear/invalidateByPrefix/size, TTL expiry, key builders, and TTL constants — all passing
• Verify NFT gallery does not re-fetch on tab switch within 5-minute window
• Verify balance updates within 30 seconds after a transaction
• Verify positions re-fetch after stake/unstake (cache is invalidated)
• Verify cache clears on wallet disconnect

Closes #374

[drips-wave]

@0xjerah Great news! 🎉 Based on an automated assessment of this PR, the linked Wave issue(s) no longer count against your application limits.

You can now already apply to more issues while waiting for a review of this PR. Keep up the great work! 🚀

Learn more about application limits