feat: wrap wallet events API (apply_update returning events)

[darioAnongba]

Summary

BDK 2.2.0 added WalletEvent returned from apply_update. Wrap this so JS consumers can react to wallet state changes (new transactions, confirmations, etc.).

References

• BDK 2.2.0 release notes
• PR: feat: Return wallet events when applying updates (#310)

Tasks

• Wrap WalletEvent type for WASM
• Update Wallet::apply_update to return events
• Add TypeScript types/examples for event handling
• Add tests