chore: RDEPUBBackgroundTrace 日志默认关闭

Release 构建下完全静默（isEnabled 固定 false），
Debug 构建下通过 _enabled 开关控制，默认开启。

Co-Authored-By: Claude <noreply@anthropic.com>

Sources/RDReaderView/EPUBUI/ReaderController/ChapterRuntime/RDEPUBBackgroundTrace.swift

@@ -2,8 +2,18 @@ import Foundation
 
 enum RDEPUBBackgroundTrace {
 
-    static func log(_ scope: String, _ message: String) {
+    static var isEnabled: Bool {
+#if DEBUG
+        return _enabled
+#else
+        return false
+#endif
+    }
 
+    static var _enabled = true
+
+    static func log(_ scope: String, _ message: String) {
+        guard isEnabled else { return }
         let threadRole = Thread.isMainThread ? "main" : "bg"
 
         let threadName = resolvedThreadName()
@@ -13,7 +23,7 @@ enum RDEPUBBackgroundTrace {
     }
 
     static func measure<T>(_ scope: String, _ message: String, work: () throws -> T) rethrows -> T {
-
+        guard isEnabled else { return try work() }
         let startedAt = CFAbsoluteTimeGetCurrent()
         log(scope, "START \(message)")
         do {