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/service/log_cleanup_service.go

@@ -197,9 +197,3 @@ func NewLogService(
 	}
 }
 
-// GetLogCleanupServiceFromApp 从应用中获取日志清理服务
-func GetLogCleanupServiceFromApp(app any) LogCleanupService {
-	// 这里需要根据实际的app结构来获取
-	// 暂时返回nil，实际使用时需要实现
-	return nil
-}