chore: update dependency management and add guardrail checks

[purplesmoke05]

📌 Description

This pull request introduces a repository guardrail test to enforce supply-chain security policies and updates several project files to comply with these new standards.

✅ Related Issues

• None

🔄 Changes

Repository guardrail enforcement and supply-chain security:

• Added tests/test_guardrail_check.py, which enforces that all Docker base images and external Compose images are pinned by digest, prohibits remote ADD and pipe-to-shell installers in Dockerfiles, and checks that the Dependabot configuration enforces a 14-day cooldown for regular updates.
• Updated .github/dependabot.yml to add a cooldown policy of 14 days for all managed ecosystems, explicitly define Docker and Docker Compose update blocks, and ensure all images are grouped and pinned by digest.

Docker and Compose image pinning:

• Changed all Docker base images and Compose service images (Dockerfile, tests/Dockerfile_unittest, tests/Dockerfile_anvil, docker-compose.yml) to use digests instead of tags, ensuring reproducible builds and improved supply-chain security.

📌 Checklist

• I have added tests where necessary.
• I have updated the documentation where necessary.

[github-actions]

Coverage Report •

File	Stmts	Miss	Branch	BrPart	Cover	Missing
tests
test_guardrail_check.py	133	133	62	62	0%	20–24, 26–27, 29–33, 39, 50–51, 57, 61, 63–64, 67–69, 73–74, 85–86, 97–100, 102, 106–108, 111–113, 116–120, 122–123, 126–127, 130–133, 137, 141–143, 145, 150–153, 157, 161–167, 169–170, 172–174, 177–178, 180–186, 190, 194–200, 202–206, 208–216, 218–221, 224, 227–233, 238–239, 243, 247–248, 250–252, 254, 260–261, 263–264, 266, 272–273, 277–278
TOTAL	37234	1450	3490	637	96%

Tests	Skipped	Failures	Errors	Time
1276	0 💤	0 ❌	0 🔥	11m 42s ⏱️

[purplesmoke05]

Added comments above the guardrail tests and helper functions to make their purpose clear.