fix(ws): guard client config updates

[Zhang-986]

Summary

• add a dedicated config mutex for WebSocket client config updated by configure
• read ping/reconnect settings through snapshots before using them from background loops
• snapshot connection state before pingLoop reads serviceID, without holding the connection mutex while writing to the socket

This intentionally does not reuse the existing c.mu for configure: connect holds c.mu while calling getConnURL, and getConnURL can call configure when the bootstrap endpoint returns ClientConfig. Reusing c.mu there would risk deadlocking that path.

Fixes #188
Fixes #189

Tests

• go test -race ./ws -run TestPingLoopConfigureRace -count=1
• go test -race ./ws -count=1
• go test ./ws -count=1
• go test ./... -count=1
• git diff --check