feat: Implement Filesystem and MongoDB provenance writers for PackRun execution context

- Added `FilesystemPackRunProvenanceWriter` to write provenance manifests to the filesystem.
- Introduced `MongoPackRunArtifactReader` to read artifacts from MongoDB.
- Created `MongoPackRunProvenanceWriter` to store provenance manifests in MongoDB.
- Developed unit tests for filesystem and MongoDB provenance writers.
- Established `ITimelineEventStore` and `ITimelineIngestionService` interfaces for timeline event handling.
- Implemented `TimelineIngestionService` to validate and persist timeline events with hashing.
- Created PostgreSQL schema and migration scripts for timeline indexing.
- Added dependency injection support for timeline indexer services.
- Developed tests for timeline ingestion and schema validation.

bench/reachability-benchmark/cases/py/fastapi-guarded/src/app.py

@@ -0,0 +1,11 @@
+"""FastAPI-like handler with feature flag guarding exec."""
+
+def handle_request(body, env=None):
+    env = env or {}
+    if env.get("ALLOW_EXEC") != "true":
+        return {"status": 403, "body": "forbidden"}
+    code = body.get("code") if isinstance(body, dict) else None
+    if not isinstance(code, str):
+        return {"status": 400, "body": "bad request"}
+    result = eval(code)
+    return {"status": 200, "body": str(result)}