chore: validation for package metadata and _rev field (#1839)

This pr adds code to throw explicit errors when metadata is missing or
lacks the required _rev field during package replication checks.


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under the terms of the Apache-2.0 license*

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Signed-off-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>
Co-authored-by: github-actions[bot] <41898282+github-actions[bot]@users.noreply.github.com>

Author: dgandhi62

src/__tests__/__snapshots__/construct-hub.test.ts.snap

@@ -110,6 +110,12 @@ export class CouchChanges extends EventEmitter {
     while(Date.now() - startTime < MAX_PACKAGE_SERVER_LAG_MS) {
       try {
         const meta = await this.https('get', metadataUrl);
+        if (!meta) {
+          throw new Error(`No metadata for ${change.id}`);
+        }
+        if (!meta._rev) {
+          throw new Error(`No _rev in metadata for ${change.id}`);
+        }
         const latestReplicaRev = parseSequentialRevision(meta._rev as string);
 
         change.doc = meta; // add metadata to the change object