[codex] Implement Bybit spot WebSocket subscriptions

[createMonster]

Summary

• implement Bybit spot subscribe_market_data using the shared Tungstenite/Reconnect WebSocket path
• generate valid Bybit V5 spot stream topics for ticker, trades, order book, and klines
• decode real Bybit spot WebSocket payloads into connector events and forward them as unified market data

Root Cause

Bybit spot exposed WebSocket URLs and codec scaffolding, but subscribe_market_data still returned a placeholder "not implemented" error. The existing stream helper also emitted the wrong order book topic shape.

Validation

• cargo fmt --all -- --check
• cargo clippy --all-targets --all-features -- -D warnings
• cargo test --all-features
• cargo audit
• cargo doc --no-deps --document-private-items --all-features
• cargo run

Closes #18