Add firewall negative integration tests for control-plane validation

[shivamp6265]

Summary

Add comprehensive end-to-end negative integration tests for the LionsOS firewall control plane. The test suite validates the HTTP API's rejection of invalid requests and ensures firewall state remains unchanged when errors occur.

Problem

The firewall's Docker runtime test suite (autotest.sh) provides good coverage of successful operations (traffic flows, rule application, route addition/removal). However, it lacks coverage of error paths and negative cases:

• Invalid interface indices
• Malformed or incomplete payloads
• Duplicate rules and routes
• Non-existent resource deletions
• Invalid protocol strings

This leaves critical input-validation code paths untested and creates regression risk when modifying the firewall's API layer or firewall services.

Solution

Add negative_tests.sh, a standalone shell script that:

1. Tests invalid requests against all major control-plane endpoints
2. Verifies the API returns appropriate error responses
3. Asserts that firewall state (route/rule counts, configuration) is unchanged
4. Cleans up any transient test state
5. Works within the existing Docker/QEMU firewall testing harness

Testing

The script can be run inside the firewall test container:

cd examples/firewall/docker
docker build -t lionsos-firewall .
docker run -it --rm -v $(pwd):/lionsos lionsos-firewall bash

# Inside container:
cd /lionsos/examples/firewall/docker
bash scripts/firewall_configuration.sh
bash scripts/building_running.sh &
sleep 10
bash scripts/negative_tests.sh

Files Changed

•  examples/firewall/docker/scripts/negative_tests.sh  (new, 142 lines)

Addresses

Closes #277