Browser Extension (Chrome MV3) compatibility: wallet.sync() fails due to CSP restrictions

## Browser Extension (Chrome MV3) Compatibility Issue

### 🐛 Problem

I'm building a Zcash wallet browser extension using WebZjs, but encountering compatibility issues with **Chrome Manifest V3's strict Content Security Policy (CSP)**.

### 🔍 Details

**Environment:**
- Chrome Extension with Manifest V3
- `@chainsafe/webzjs-wallet` (latest version)
- Zcash testnet
- CSP: `script-src 'self' 'wasm-unsafe-eval'`

**Issue:**

Chrome MV3 disallows `eval()` and `new Function()` for security reasons. This breaks WebZjs's sync mechanism:

// ❌ Fails in Chrome MV3
await wallet.sync();
// Error: eval() is not allowed in Chrome extensions

await initThreadPool(8);
// Error: Web Workers cannot use eval()**Root cause:**
- `wallet.sync()` spawns Web Workers using `eval()` internally
- `initThreadPool()` also relies on `eval()` for multi-threading
- Chrome MV3 CSP blocks these operations

### 🔧 Current Workaround

I've implemented a **custom sync** using CipherScan's WASM for client-side decryption:

// ✅ Works: Custom sync with WASM
const compactBlocks = await fetchCompactBlocks(startHeight, endHeight);
const matches = await batch_filter_compact_outputs(compactBlocks, viewingKey);
const balance = calculateBalance(matches); // 0.02 ZEC ✅**However**, this creates a critical issue:

// WebZjs's internal database is EMPTY (never synced)
await wallet.propose_transfer(accountId, toAddress, amount);
// ❌ Error: "insufficient balance" (WebZjs DB has no notes!)**The problem:**
- Custom sync finds funds ✅
- WebZjs DB remains empty ❌
- `propose_transfer()` can't find notes to spend ❌

### ❓ Questions

Is there a way to:

1. **Use WebZjs sync in single-threaded mode** (without eval/Web Workers)?
- Does WebZjs have a fallback sync mechanism compatible with MV3?

2. **Manually populate WebZjs database** with notes from custom sync?
- Can we inject notes/nullifiers into WebZjs's internal DB?

3. **Use alternative transaction API** (PCZTs?) that doesn't require DB sync?
// Does this work without wallet.sync()?
const pczt = await wallet.pczt_create(accountId, toAddress, value);
### 💡 Why This Matters

Browser extensions are a **common use case** for crypto wallets (Metamask, Phantom, Rabby, etc.). Chrome MV3 is now **mandatory** for all new extensions.

Making WebZjs compatible with MV3 would:
- ✅ Enable Zcash browser wallet extensions
- ✅ Improve Zcash ecosystem adoption
- ✅ Align with industry standards (all major wallets support MV3)

### 📝 Reproduction Steps

1. Create Chrome Extension (Manifest V3)
2. Add CSP: `"content_security_policy": { "extension_pages": "script-src 'self' 'wasm-unsafe-eval'; object-src 'self'" }`
3. Initialize WebZjs: `const wallet = new WebWallet("test", lightwalletdUrl, 10);`
4. Try to sync: `await wallet.sync();` → **Fails with CSP error**

### 🙏 Request

Any guidance on MV3-compatible sync or transaction building would be greatly appreciated!