fix(reference): preserve observed directories and unreadable links

Continue validating child directories observed before a parent enumeration failure. Reconcile unobserved link targets at the reader using canonical path identity and the nearest failed ancestor, preserving exclusions and cancellation.

Refs: #4013, #4053, #4060

Co-authored-by: XY-code1 <1611761391@qq.com>

src/reference/ReferenceSourceReaderTypes.ts

@@ -93,6 +93,10 @@ export type TraversalState = {
     kind: ReferenceSourceExclusionKind,
   ) => boolean;
   readonly entries: ReferenceSourceEntry[];
+  readonly exclusions: Array<{
+    readonly path: string;
+    readonly kind: ReferenceSourceExclusionKind;
+  }>;
   readonly pending: PendingDirectory[];
   bytesRead: number;
 };