[Core & Milky] Implement group_invitation event

[Szzrain]

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[Copilot]

Pull Request Overview

This PR implements a new group_invitation event system to handle group invitation notifications in both Core and Milky modules. The implementation adds event handling for when a bot receives group invitations through light app messages.

• Adds new event classes and data structures for group invitations
• Implements event parsing logic for light app messages containing group invitations
• Integrates the new event into the existing event service and JSON serialization system

Reviewed Changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
Lagrange.Core/Events/EventArgs/BotGroupInvitationEvent.cs	New event class for group invitation events
Lagrange.Core/Message/Entities/LightAppEntity.cs	New message entity for parsing light app messages
Lagrange.Core/Internal/Logic/PushLogic.cs	Added logic to detect and parse group invitation messages
Lagrange.Milky/Entity/Event/GroupInvitationEvent.cs	Event data structure for Milky API
Lagrange.Milky/Utility/EntityConvert.Event.cs	Conversion logic between Core and Milky events
Lagrange.Milky/Event/EventService.cs	Event service registration and handling
Lagrange.Milky/Utility/JsonUtility.cs	JSON serialization registration
Lagrange.Milky/Utility/EntityConvert.Segment.cs	Segment conversion for light app messages

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[Executor-Cheng]

谢谢dalao