[mock-chronik-client] Match shape of subs in ws to ChronikClientNode for ChronikClientNode methods

Summary:
ChronikClientNode supports multiple types of ws subscription, so ws.subs is an object, not an array.

Match this shape for in-node users.

token-server uses in-node chronik-client but tests legacy shape to match mock behavior. Update token-server to test correct behavior.

Test Plan: npm test

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D15697