Use exported Citus requirements in test images

[ihalatci]

Summary

• replace the shared test-image Python dependency input with the exported requirements from the Citus failure-test environment
• move the test-image Python runtime from 3.8 to 3.12 so upstream mitmproxy 12.2.2 can be installed
• keep the image test runner aligned with the refreshed dependency set

Context

This supports the Citus dependency refresh and the switch away from the forked mitmproxy reference in the test environment.

Verification

• installed the shared test-image requirements in a clean Python 3.12 environment
• confirmed the resolved versions include mitmproxy 12.2.2, cryptography 46.0.7, pytest 9.0.3, Werkzeug 3.1.6, and tornado 6.5.5

[ihalatci]

Superseded: these test-image dependency updates are being moved to the-process repo instead.