Refactor and modernise DRep golden tests for thread-safety

[newhoggy]

Changelog

- description: |
    Refactor and modernise `DRep` golden tests for thread-safety
# uncomment types applicable to the change:
  type:
  # - feature        # introduces a new feature
  # - breaking       # the API has changed in a breaking way
  - compatible     # the API has changed but is non-breaking
  # - optimisation   # measurable performance improvements
  # - refactoring    # QoL changes
  - bugfix         # fixes a defect
  # - test           # fixes/modifies tests
  # - maintenance    # not directly related to the code
  # - release        # related to a new release preparation
  # - documentation  # change in code docs, haddocks...

Context

This PR improves the structure and exception safety of golden tests related to DRep governance features by:

• Replacing Property-based Hedgehog tests with a new UnitIO style enabled by Hedgehog.Extras.Test.New.Monad from hedgehog-extras, which simplifies composition and improves readability.
• Extracting serveFilesWhile to two new modules:
  • Test.Cardano.CLI.Network (used in traditional test code)
  • Test.Cardano.CLI.New.Network (uses MonadMask, preferred in the new-style tests)

Dependency Update

Updates the hedgehog-extras dependency, for the new support for the UnitIO abstraction and new test monads.

Benefits

• Clearer test structure and improved type safety via UnitIO.
• Better exception handling guarantees using MonadMask.
• Isolated network test utilities support both legacy and modern test styles.

How to trust this PR

Highlight important bits of the PR that will make the review faster. If there are commands the reviewer can run to observe the new behavior, describe them.

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated. See Running tests for more details
• Self-reviewed the diff

[carbolymer]

I think we should keep watchdogs everywhere.

[newhoggy]

We will need to write a new watchdog for the new test api. I wanted to see it hang in one of these property test first before adding it.

[Jimbo4350]

I'm not convinced this refactor is necessary. Let's explore other options.

[github-actions]

This PR is stale because it has been open 45 days with no activity.