Refactor: Remove NFStream and flow identity utilities; introduce Tshark manager

- Deleted flow_identity.py and nfstream_flow_worker.py as they are no longer needed.
- Removed nfstream_manager.py and its associated logic for managing NFStream workers.
- Added tshark_manager.py to manage tshark packet enrichment and matching.
- Updated setup_build_server.sh to include default environment variables for tshark.
- Implemented packet signature generation and enrichment logic in the new TsharkManager class.

backend/requirements.txt

@@ -12,7 +12,6 @@ pydantic==2.12.3
 pydantic_core==2.41.4
 pyroute2==0.9.5
 python-multipart==0.0.22
-nfstream==6.5.4
 scapy==2.6.1
 sniffio==1.3.1
 starlette==0.48.0