timeseries, multimodal: addressed Bandit findings (#2347)

This PR aims to address Bandit findings in the multimodal sample by tightening environment-variable handling in the weld data simulator and suppressing Bandit warnings in functional tests.

Changes:

- Add input validation helpers for key environment variables used to build the RTSP URL and connect to MQTT in the weld data simulator.
- Annotate many functional-test assert statements with # nosec B101 and remove an unused subprocess import.
- Ignore Python __pycache__/ at the repo root for the multimodal sample

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: vkb1 <19564820+vkb1@users.noreply.github.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: 3 people

manufacturing-ai-suite/industrial-edge-insights-multimodal/.gitignore

@@ -11,6 +11,7 @@ helm-packages/
 .venv/
 
 # Python cache
+__pycache__/
 tests/**/__pycache__/
 tests/__pycache__/
 tests/functional/tests.log