[Core & Milky] Implement friend_request event

[Szzrain]

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[Copilot]

Pull Request Overview

This PR implements support for the friend_request event, adding the ability to detect and handle incoming friend requests in the Lagrange chat system. The implementation spans both the Core and Milky components, providing end-to-end event processing from protocol-level packet handling to JSON serialization for external consumers.

Key changes:

• Added protocol-level packet structures and parsing for friend request notifications
• Implemented event data classes and conversion utilities for friend request events
• Extended the event service to handle and serialize friend request events for external consumption

Reviewed Changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
Lagrange.Core/Internal/Packets/Notify/FriendRequest.cs	Defines protobuf packet structures for friend request notifications
Lagrange.Core/Events/EventArgs/BotFriendRequestEvent.cs	Core event class containing friend request data
Lagrange.Core/Internal/Logic/PushLogic.cs	Adds packet parsing logic for Event0x210 friend request notifications
Lagrange.Milky/Entity/Event/FriendRequestEvent.cs	JSON-serializable event classes for external API
Lagrange.Milky/Utility/EntityConvert.Event.cs	Conversion logic from core events to Milky events
Lagrange.Milky/Event/EventService.cs	Event handler registration and processing for friend requests
Lagrange.Milky/Utility/JsonUtility.cs	JSON serialization context registration for friend request events

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