feat(wasm-utxo): export testutils module

Add testutils namespace export to the main index.ts file to make test
utilities available to consumers of the library.

Issue: BTC-2980

Co-authored-by: llm-git <llm-git@ttll.de>

Author: OttoAllmendinger

packages/wasm-utxo/js/index.ts

@@ -14,6 +14,7 @@ export * as utxolibCompat from "./utxolibCompat.js";
 export * as fixedScriptWallet from "./fixedScriptWallet/index.js";
 export * as bip32 from "./bip32.js";
 export * as ecpair from "./ecpair.js";
+export * as testutils from "./testutils/index.js";
 
 // Only the most commonly used classes and types are exported at the top level for convenience
 export { ECPair } from "./ecpair.js";