fix: Detect demo-format WS auth ack (success:true) as success (#63)

[darekurlik]

Problem

WebsocketStreamClientImpl.onMessage only treats "retCode":0 as a successful auth ack:

isAuthenticated = msg.contains("\"retCode\":0");

Bybit's demo trading private WebSocket (wss://stream-demo.bybit.com/v5/private) instead responds with:

{"req_id":"...","success":true,"ret_msg":"","op":"auth","conn_id":"..."}

No retCode field → lib reports "Authentication failed." and never flushes queued private subscriptions (order / position / execution / wallet), leaving the WS open but useless.

This is the same issue reported in #63.

Fix

Accept either signal as auth success:

isAuthenticated = msg.contains("\"retCode\":0")
        || (msg.contains("\"success\":true") && msg.contains("\"op\":\"auth\""));

Mainnet acks (which include retCode:0) keep working unchanged.

Verified

End-to-end against real Bybit demo with valid demo credentials:

Sent Auth: {"op":"auth","args":["...",1777463210561,"..."]}
WS msg:    {"success":true,"op":"auth","conn_id":"..."}
→ Authentication successful.
Sent Subscribe: {"op":"subscribe","args":["order","position","execution","wallet"]}
WS msg:    {"success":true,"op":"subscribe",...}

Closes #63.