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/middleware/ratelimit.go

@@ -75,27 +75,6 @@ func (rl *RateLimiter) isAllowed(key string) bool {
 	return true
 }
 
-func (rl *RateLimiter) count(key string) int {
-	rl.mu.Lock()
-	defer rl.mu.Unlock()
-
-	now := time.Now()
-	times := rl.requests[key]
-
-	var valid []time.Time
-	for _, t := range times {
-		if now.Sub(t) < rl.window {
-			valid = append(valid, t)
-		}
-	}
-	rl.requests[key] = valid
-	return len(valid)
-}
-
-func RateLimit(requestsPerMinute int) gin.HandlerFunc {
-	return RateLimitWithDuration(requestsPerMinute, time.Minute)
-}
-
 func RateLimitWithDuration(limit int, window time.Duration) gin.HandlerFunc {
 	limiter := NewRateLimiter(limit, window)
 
@@ -115,32 +94,6 @@ func RateLimitWithDuration(limit int, window time.Duration) gin.HandlerFunc {
 	}
 }
 
-func RateLimitWithKey(requestsPerMinute int, keyFunc func(c *gin.Context) string) gin.HandlerFunc {
-	return RateLimitWithDurationAndKey(requestsPerMinute, time.Minute, keyFunc)
-}
-
-func RateLimitWithDurationAndKey(limit int, window time.Duration, keyFunc func(c *gin.Context) string) gin.HandlerFunc {
-	limiter := NewRateLimiter(limit, window)
-
-	return func(c *gin.Context) {
-		key := keyFunc(c)
-		if key == "" {
-			key = c.ClientIP()
-		}
-
-		if !limiter.isAllowed(key) {
-			c.JSON(http.StatusTooManyRequests, gin.H{
-				"code":    429,
-				"message": "too many requests, please try again later",
-			})
-			c.Abort()
-			return
-		}
-
-		c.Next()
-	}
-}
-
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