feat: 架构整改 — Context拆分、Runtime拆分、异步章节加载、UI测试覆盖

Phase 1: Context 拆分
- 新增 RDEPUBReaderState/RDEPUBReaderEnvironment/RDEPUBReaderServices
- RDEPUBReaderContext 改为过渡门面，代理到 State/Environment/Services

Phase 2: Runtime 拆分
- 新增 RDEPUBPresentationRuntime 处理分页状态管理
- 新增 RDEPUBChapterWarmupOrchestrator 处理章节预热与加载编排
- RDEPUBReaderRuntime 从 1277 行收缩，公共 API 转发到新 facade

Phase 0.5: 性能优化
- prepareOnDemandChapter 支持异步模式（allowSynchronousLoad: false）
- extendPartialBookPageMapIfNeeded 改为 DispatchGroup 并发加载
- RDEPUBChapterOffsetMap.cfiMap 加 NSLock 保护数据竞争
- CFI Map 构建延迟到后台队列（scheduleDeferredCFIMapBuildIfNeeded）
- RDEPUBTextPageRenderView 引入静态位图缓存
- RDEPUBTextContentView 新增 loadingSpinner 占位页

Phase 3: 状态机
- 新增 RDEPUBNavigationStateMachine（含 DEBUG 合法转换校验）
- 新增 RDEPUBPaginationState 记录分页来源

Review 修复
- makeSummary 重复方法合并
- ensureNavigationTargetAvailable 同步路径加注释标记

UI 测试
- 新增 AsyncChapterLoadingTests（20 个测试，覆盖全部架构整改场景）
- 跨章节翻页、延迟 CFI、状态机、内存警告、预加载、位置恢复等

Sources/RDReaderView/EPUBUI/RDEPUBReaderController+DataSource.swift

@@ -1,7 +1,27 @@
 
 import UIKit
 
-extension RDEPUBReaderController: RDReaderDataSource, RDReaderDelegate {
+extension RDEPUBReaderController: RDReaderDataSource, RDReaderPageProvider, RDReaderDelegate {
+
+    public func numberOfPages(in readerView: RDReaderView) -> Int {
+        pageCountOfReaderView(readerView: readerView)
+    }
+
+    public func readerView(_ readerView: RDReaderView, viewForPageAt index: Int, reusableView: UIView?) -> UIView {
+        pageContentView(readerView: readerView, pageNum: index, containerView: reusableView)
+    }
+
+    public func pageIdentifier(in readerView: RDReaderView, index: Int) -> String? {
+        pageIdentifier(readerView: readerView, pageNum: index)
+    }
+
+    public func readerViewTopChrome(_ readerView: RDReaderView) -> UIView? {
+        topToolView(readerView: readerView)
+    }
+
+    public func readerViewBottomChrome(_ readerView: RDReaderView) -> UIView? {
+        bottomToolView(readerView: readerView)
+    }
 
     public func pageCountOfReaderView(readerView: RDReaderView) -> Int {
         readerContext.bookPageMap?.totalPages ?? textBook?.pages.count ?? activePages.count
@@ -9,7 +29,10 @@ extension RDEPUBReaderController: RDReaderDataSource, RDReaderDelegate {
 
     public func pageContentView(readerView: RDReaderView, pageNum: Int, containerView: UIView?) -> UIView {
         if readerContext.bookPageMap != nil {
-            _ = runtime.prepareOnDemandChapter(forAbsolutePageNumber: pageNum + 1)
+            _ = runtime.prepareOnDemandChapter(
+                forAbsolutePageNumber: pageNum + 1,
+                allowSynchronousLoad: false
+            )
             if let resolvedPage = runtime.pageResolver.resolvePage(absolutePageIndex: pageNum) {
                 let contentView = (containerView as? RDEPUBTextContentView) ?? RDEPUBTextContentView()
                 contentView.delegate = self
@@ -34,6 +57,24 @@ extension RDEPUBReaderController: RDReaderDataSource, RDReaderDelegate {
                 )
                 return contentView
             }
+
+            let contentView = (containerView as? RDEPUBTextContentView) ?? RDEPUBTextContentView()
+            contentView.delegate = self
+            readerView.registerSelectionGestureDependenciesIfNeeded(for: contentView)
+            contentView.selectionTapSuppressionDidChange = { [weak readerView, weak contentView] isSuppressed in
+                guard let readerView, let contentView else { return }
+                readerView.updateSelectionTapSuppression(for: contentView, isSuppressed: isSuppressed)
+            }
+            contentView.selectionPagingSuppressionDidChange = { [weak readerView, weak contentView] isSuppressed in
+                guard let readerView, let contentView else { return }
+                readerView.updateSelectionPagingSuppression(for: contentView, isSuppressed: isSuppressed)
+            }
+            contentView.configureLoading(
+                pageNumber: pageNum + 1,
+                totalPages: pageCountOfReaderView(readerView: readerView),
+                configuration: configuration
+            )
+            return contentView
         }
 
         if let textBook, let page = textBook.page(at: pageNum + 1) {
@@ -307,7 +348,10 @@ extension RDEPUBReaderController: RDReaderDataSource, RDReaderDelegate {
         }
 
         if readerContext.bookPageMap != nil {
-            _ = runtime.prepareOnDemandChapter(forAbsolutePageNumber: effectivePageNum + 1)
+            _ = runtime.prepareOnDemandChapter(
+                forAbsolutePageNumber: effectivePageNum + 1,
+                allowSynchronousLoad: false
+            )
             runtime.extendPartialBookPageMapIfNeeded(currentPageNumber: effectivePageNum + 1)
         }