Improve Testing for libjs

### Is your feature request related to a problem?

we are missing some integration, unit tests, api tests more like demo tests.

### Describe the solution you'd like

Add tests for

- [ ] transaction_sender.js
- [ ] api ( some api are remaining)
- [x] Api test , some test showing different ways to use libjs

### Additional context

For testing absinthe socket, we can replace windows socket. more here
https://github.com/phoenixframework/phoenix/blob/main/assets/test/socket_test.js

Start by reviewing transaction_sender.js and the remaining API surface, then compare the socket-testing approach in Phoenix's assets/test/socket_test.js. Done means adding the requested integration, unit, API, and demo-style coverage, including a way to replace the Windows socket for Absinthe socket testing.

Written by the indexing model from the issue text.