Add sample proof bundle configurations and verification script

- Introduced sample proof bundle configuration files for testing, including `sample-proof-bundle-config.dsse.json`, `sample-proof-bundle.dsse.json`, and `sample-proof-bundle.json`.
- Implemented a verification script `test_verify_sample.sh` to validate proof bundles against specified schemas and catalogs.
- Updated existing proof bundle configurations with new metadata, including versioning, created timestamps, and justification details.
- Enhanced evidence entries with expiration dates and hashes for better integrity checks.
- Ensured all new configurations adhere to the defined schema for consistency and reliability in testing.

tests/Vex/ProofBundles/cas/coverage.json

@@ -0,0 +1,16 @@
+{
+  "tool": "reach-cov",
+  "entrypoints": [
+    {
+      "id": "app://api/GET-/healthz",
+      "coverage_percent": 96.3,
+      "negative_tests": true
+    },
+    {
+      "id": "app://worker/queue/default",
+      "coverage_percent": 95.1,
+      "negative_tests": true
+    }
+  ],
+  "timestamp": "2025-12-03T23:50:00Z"
+}