fix(cache): make Zip-source caches atomic and robust to partial state

Follow-up to the GitHubStream cache fixes. The same poisoned-cache
class existed in the GitHubDownload path and a few related spots:

- GitHubDownload.download: wipe pre-existing state before extracting
  and write a .anon-complete marker only after a successful extract.
  On error, rm the partial cache so a retry starts clean. getFileContent
  and getFiles now gate on the marker instead of "any file/folder
  exists," so a half-extracted tree can never be served as canonical.
- GitHubDownload.getFileContent: validate cached file size against the
  upstream FileModel size (via the new AnonymizedFile.size()), same
  guard as GitHubStream. getFiles filters the marker from the listing.
- FileSystem.listFiles: drop the bogus stats.ino.toString() as sha.
  An inode isn't a content hash; anything comparing it to a Git blob
  sha would silently disagree. Leave undefined.
- S3.write: remove the fire-and-forget data.on("error") -> this.rm(...).
  Multipart Upload doesn't commit partial objects, so there was nothing
  to clean up, and the handler raced retries and could delete a
  previously-good object on a transient source-stream hiccup. The
  size-validated read path recovers from any other undersized objects.
- GitHubStream.resolveLfsPointer: drop the post-decision early-return
  in blobStream.on("error"). Currently redundant with the inner
  listener, but removes the future-refactor footgun.

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

src/core/source/GitHubStream.ts

@@ -114,7 +114,10 @@ export default class GitHubStream extends GitHubBase {
     });
     blobStream.on("end", () => decide());
     blobStream.on("error", (err) => {
-      if (decided) return;
+      // Always propagate — pre-decision this is the only listener; once a
+      // non-LFS decision is made, the inner branch attaches its own
+      // listener that will also fire, but we shouldn't rely on that being
+      // there if the code is later refactored.
       decided = true;
       out.destroy(err);
     });