feat(auth): 优化注册功能并添加注册异常处理

- 新增 RegistrationException 类用于处理注册相关的异常
- 在全局异常处理器中添加 RegistrationException 的处理逻辑
- 修改用户服务中的注册逻辑，当用户名或邮箱已存在时抛出 RegistrationException
- 更新注册码实体类，将日期时间字段改为字符串类型
- 调整注册码生成和验证逻辑，使用字符串格式的日期时间

biji-houdaun/src/main/java/com/test/bijihoudaun/entity/RegistrationCode.java

@@ -7,7 +7,6 @@ import io.swagger.v3.oas.annotations.media.Schema;
 import lombok.Data;
 
 import java.io.Serializable;
-import java.time.LocalDateTime;
 
 @Data
 @TableName("registration_codes")
@@ -24,11 +23,51 @@ public class RegistrationCode implements Serializable {
     private String code;
 
     @Schema(description = "过期时间", name = "expiryTime")
-    private LocalDateTime expiryTime;
+    private String expiryTime;
 
     @Schema(description = "创建者", name = "createdBy")
     private String createdBy;
 
     @Schema(description = "创建时间", name = "createdAt")
-    private LocalDateTime createdAt;
+    private String createdAt;
+
+    public Long getId() {
+        return id;
+    }
+
+    public void setId(Long id) {
+        this.id = id;
+    }
+
+    public String getCode() {
+        return code;
+    }
+
+    public void setCode(String code) {
+        this.code = code;
+    }
+
+    public String getExpiryTime() {
+        return expiryTime;
+    }
+
+    public void setExpiryTime(String expiryTime) {
+        this.expiryTime = expiryTime;
+    }
+
+    public String getCreatedBy() {
+        return createdBy;
+    }
+
+    public void setCreatedBy(String createdBy) {
+        this.createdBy = createdBy;
+    }
+
+    public String getCreatedAt() {
+        return createdAt;
+    }
+
+    public void setCreatedAt(String createdAt) {
+        this.createdAt = createdAt;
+    }
 }