Some unit tests in the CI are flaky

[jpraynaud]

Why

We have noticed that some folder collisions occur in the unit tests and create flakiness in the CI:

• https://github.com/input-output-hk/mithril/actions/runs/13760339435/job/38474910295#step:5:1812
• https://github.com/input-output-hk/mithril/actions/runs/13760339435/job/38475799700
• https://ci.iog.io/build/6981859/nixlog/1
• https://ci.iog.io/build/6982029/nixlog/1

What

Investigate and fix the flakiness.

How

• Investigate the flakiness
• Create a fix:
  • Add a parameter to the initialize_dependencies function with a temporary directory
  • Use a macro to automatically compute a unique folder for each test