[chronik-client] More robust integration test for websocket.ts

Summary:
Seeing occasional flakiness failure of this test related to msgCollector being populated out of sync with test inspection.

Implement same solution used to address this issue on the token websocket tests (e.g. token_alp.ts).

Test Plan: CI test

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D16211