[Core & Milky] Implement group_member_increase event

[kengwang]

No description provided.

[Copilot]

Pull Request Overview

This PR implements the group_member_increase event to handle when new members join a group. The implementation follows the existing pattern for similar events like group_member_decrease.

• Adds BotGroupMemberIncreaseEvent event class with group, member, invitor, and operator information
• Implements event handling logic in PushLogic to process group member increase notifications
• Adds Milky layer conversion and serialization support for the new event

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
Lagrange.Core/Events/EventArgs/BotGroupMemberIncreaseEvent.cs	New event class for group member increase events
Lagrange.Core/Internal/Logic/PushLogic.cs	Adds handling logic for group member increase notifications
Lagrange.Milky/Entity/Event/GroupMemberIncreaseEvent.cs	Milky layer event entity for JSON serialization
Lagrange.Milky/Utility/EntityConvert.Event.cs	Conversion method from core event to Milky event
Lagrange.Milky/Utility/JsonUtility.cs	JSON serialization support for the new event
Lagrange.Milky/Event/EventService.cs	Event service registration and handling

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