Improve path parameter validation in `api_validator`

Current Limitation

Refer https://github.com/wso2/api-platform/pull/177#discussion_r2558409738

Suggested Improvement

 // validatePathParameters checks if path parameters have balanced braces
 func (v *APIValidator) validatePathParameters(path string) bool {
-	openCount := strings.Count(path, "{")
-	closeCount := strings.Count(path, "}")
-	return openCount == closeCount
+	depth := 0
+	for _, ch := range path {
+		if ch == '{' {
+			depth++
+			if depth > 1 {
+				return false // nested braces not allowed
+			}
+		} else if ch == '}' {
+			depth--
+			if depth < 0 {
+				return false // closing before opening
+			}
+		}
+	}
+	return depth == 0 // all braces must be closed
 }

Version

No response