v4.7.8: Add p2p chat endpoints for bybit rest api

What's Changed

• feat(v4.7.8): add p2p chat endpoints for bybit rest api by @tiagosiebler in #573

Context

Add the following endpoints to the REST client:

• getP2PChatSessions() - List P2P chat sessions with cursor pagination and read-status filtering.
• getP2PChatSessionId() - Get the encrypted chat session ID for a counterparty.
• sendP2PChatMessage() - Send a message in a P2P chat session.
• getP2PChatMessages() - List P2P chat messages, newest first.

Full Changelog: v4.7.7...v4.7.8