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/flask-template/src/app.py

@@ -0,0 +1,12 @@
+"""Minimal flask-like template rendering sink (reachable)."""
+
+def render(template: str, context: dict) -> str:
+    return template.replace("{{name}}", context.get("name", "guest"))
+
+def handle_request(body):
+    template = body.get("template") if isinstance(body, dict) else None
+    if not isinstance(template, str):
+        return {"status": 400, "body": "bad request"}
+    rendered = render(template, {"name": "guest"})
+    # Sink: returns rendered template (models potential SSTI)
+    return {"status": 200, "body": rendered}