refactor: cleanup unused code and simplify internal packages

This commit performs a significant cleanup of the codebase by removing unused functions, methods, and entire files across various internal modules. This reduces technical debt and simplifies the project structure.

Key changes include:
- **cache**: Removed unused cache key generators and metrics snapshots.
- **dto**: Removed redundant converter functions and segment creation helpers.
- **middleware**: Deleted the unused `logger.go` middleware and simplified `ratelimit.go` and `casbin.go`.
- **model**: Removed unused ID helpers, database closing functions, and batch decryption logic.
- **pkg**: Cleaned up unused utility functions in `circuitbreaker`, `crypto`, `cursor`, `hook`, and `utils`.
- **service**: Deleted `account_cleanup_service.go` and removed unused helper functions in `log_cleanup_service.go` and `sensitive_service.go`.
- **repository**: Removed unused private loading methods in `comment_repo.go`.

internal/dto/group_converter.go

@@ -50,26 +50,6 @@ func GroupMemberToResponse(member *model.GroupMember) *GroupMemberResponse {
 	}
 }
 
-// GroupMemberToResponseWithUser 将GroupMember转换为GroupMemberResponse（包含用户信息）
-func GroupMemberToResponseWithUser(member *model.GroupMember, user *model.User) *GroupMemberResponse {
-	if member == nil {
-		return nil
-	}
-	resp := GroupMemberToResponse(member)
-	if user != nil {
-		resp.User = ConvertUserToResponse(user)
-	}
-	return resp
-}
-
-// GroupMembersToResponse 将GroupMember列表转换为GroupMemberResponse列表
-func GroupMembersToResponse(members []model.GroupMember) []*GroupMemberResponse {
-	result := make([]*GroupMemberResponse, 0, len(members))
-	for i := range members {
-		result = append(result, GroupMemberToResponse(&members[i]))
-	}
-	return result
-}
 
 // GroupAnnouncementToResponse 将GroupAnnouncement转换为GroupAnnouncementResponse
 func GroupAnnouncementToResponse(announcement *model.GroupAnnouncement) *GroupAnnouncementResponse {