重构：将示例文件组织到子目录

修复 Go 规范问题：一个目录不能有多个 package main

文件结构调整：
- example/concurrent_example.go → example/concurrent/main.go
- example/index_example.go → example/index/main.go
- example/topic_processor_example.go → example/topic_processor/main.go

修复 API 适配：
- index/main.go: 更新为新的查询 API（移除 startIdx/endIdx 参数）
- webapp/main.go: 使用 processor.Query 方法替代 RecordQuery
  - 移除 queryCache，直接使用 processor
  - 更新查询调用，移除状态参数

文档更新：
- example/README.md: 更新所有示例的运行路径
- example/RUN_CONCURRENT.md: 更新运行命令

所有示例编译测试通过 ✅

example/webapp/main.go

@@ -8,17 +8,14 @@ import (
 	"net/http"
 	"os"
 	"strconv"
-	"sync"
 	"time"
 
 	"code.tczkiot.com/seqlog"
 )
 
 var (
-	seq         *seqlog.Seqlog
-	logger      *slog.Logger
-	queryCache  = make(map[string]*seqlog.RecordQuery)
-	queryCacheMu sync.RWMutex
+	seq    *seqlog.Seqlog
+	logger *slog.Logger
 )
 
 func main() {
@@ -522,20 +519,12 @@ func handleQuery(w http.ResponseWriter, r *http.Request) {
 		forward = 10
 	}
 
-	// 从缓存中获取或创建 query 对象
-	queryCacheMu.Lock()
-	query, exists := queryCache[topic]
-	if !exists {
-		var err error
-		query, err = seq.NewTopicQuery(topic)
-		if err != nil {
-			queryCacheMu.Unlock()
-			http.Error(w, err.Error(), http.StatusNotFound)
-			return
-		}
-		queryCache[topic] = query
+	// 获取 processor
+	processor, err := seq.GetProcessor(topic)
+	if err != nil {
+		http.Error(w, err.Error(), http.StatusNotFound)
+		return
 	}
-	queryCacheMu.Unlock()
 
 	// 获取当前处理索引和读取索引
 	startIdx := seq.GetProcessingIndex(topic)
@@ -546,7 +535,7 @@ func handleQuery(w http.ResponseWriter, r *http.Request) {
 
 	// 向后查询
 	if backward > 0 && startIdx > 0 {
-		backResults, err := query.QueryNewest(startIdx-1, backward, startIdx, endIdx)
+		backResults, err := processor.QueryNewest(startIdx-1, backward)
 		if err == nil {
 			results = append(results, backResults...)
 		}
@@ -554,7 +543,7 @@ func handleQuery(w http.ResponseWriter, r *http.Request) {
 
 	// 当前位置
 	if startIdx < endIdx {
-		currentResults, err := query.QueryOldest(startIdx, 1, startIdx, endIdx)
+		currentResults, err := processor.QueryOldest(startIdx, 1)
 		if err == nil {
 			results = append(results, currentResults...)
 		}
@@ -562,7 +551,7 @@ func handleQuery(w http.ResponseWriter, r *http.Request) {
 
 	// 向前查询
 	if forward > 0 {
-		forwardResults, err := query.QueryOldest(endIdx, forward, startIdx, endIdx)
+		forwardResults, err := processor.QueryOldest(endIdx, forward)
 		if err == nil {
 			results = append(results, forwardResults...)
 		}