feat(reader): 实现大书快速进入与增量分页路径

- PaginationCoordinator: 新增 textReflowable 快速进入路径，支持增量章节构建
  与 staged 合并策略，避免整书一次性构建的主线程阻塞
- TextBookBuilder: 重构为支持单章构建与增量合并模式
- ChapterPageCounter: 优化分页计数逻辑，支持章节级分页缓存
- PageFrameFactory: 新增 CoreText 页面帧工厂，提升排版性能
- ReaderContext/ReaderRuntime: 适配增量分页状态管理

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

Sources/RDReaderView/EPUBUI/ReaderController/RDEPUBReaderRuntime.swift

@@ -73,11 +73,15 @@ final class RDEPUBReaderRuntime {
             return false
         }
 
-        if context.textBook != nil {
-            guard let location = controller.resolvedTextLocation(forPageNumber: pageNumber) else {
+        if let textBook = context.textBook {
+            guard textBook.page(at: pageNumber) != nil else {
                 return false
             }
-            return locationCoordinator.restoreReadingLocation(location, animated: animated)
+            readerView.transitionToPage(pageNum: pageNumber - 1, animated: animated)
+            if let location = locationCoordinator.currentVisibleLocation() {
+                context.persist(location: location)
+            }
+            return true
         }
 
         guard context.activePages.indices.contains(pageNumber - 1) else {