fix: resolve unused assignment warning in material_matching_service

- Changed termination_reason from String to Option<String> to eliminate unused assignment warning
- Updated all assignments to use Some() wrapper
- Simplified default value logic using unwrap_or_else()
- Maintains same functionality while making code more idiomatic Rust

apps/desktop/src-tauri/src/business/services/material_matching_service.rs

@@ -755,7 +755,7 @@ impl MaterialMatchingService {
         let mut total_rounds = 0u32;
         let mut successful_rounds = 0u32;
         let mut global_used_segment_ids = HashSet::new();
-        let mut termination_reason = String::new();
+        let mut termination_reason: Option<String> = None;
         let mut materials_exhausted = false;
 
         // 为每个模板维护独立的序号计数器
@@ -805,7 +805,7 @@ impl MaterialMatchingService {
 
                 // 如果没有任何模板可以匹配，提前终止
                 if !any_template_can_match {
-                    termination_reason = format!("第{}轮预检查发现无任何模板可完整匹配，提前终止", total_rounds);
+                    termination_reason = Some(format!("第{}轮预检查发现无任何模板可完整匹配，提前终止", total_rounds));
                     materials_exhausted = true;
                     break;
                 }
@@ -916,7 +916,7 @@ impl MaterialMatchingService {
             // 检查是否应该继续下一轮
             if round_successful_matches == 0 {
                 // 本轮没有任何成功匹配，终止循环
-                termination_reason = format!("第{}轮无任何成功匹配，素材已耗尽", total_rounds);
+                termination_reason = Some(format!("第{}轮无任何成功匹配，素材已耗尽", total_rounds));
                 materials_exhausted = true;
                 break;
             } else {
@@ -925,15 +925,13 @@ impl MaterialMatchingService {
 
             // 可选：添加最大轮数限制，防止无限循环
             if total_rounds >= 100 {
-                termination_reason = "达到最大轮数限制(100轮)".to_string();
+                termination_reason = Some("达到最大轮数限制(100轮)".to_string());
                 break;
             }
         }
 
         // 设置默认终止原因（如果没有设置）
-        if termination_reason.is_empty() {
-            termination_reason = "正常完成".to_string();
-        }
+        let final_termination_reason = termination_reason.unwrap_or_else(|| "正常完成".to_string());
 
         // 计算汇总信息
         let summary = self.calculate_batch_summary(&matching_results);
@@ -949,7 +947,7 @@ impl MaterialMatchingService {
             summary,
             total_rounds,
             successful_rounds,
-            termination_reason,
+            termination_reason: final_termination_reason,
             materials_exhausted,
         })
     }