refactor(stm): Reuse the cached unsafe SRS in the SNARK test setups

[damrobi]

Content

This PR includes an update to the way we use the unsafe SNARK setup in tests in order to reduce the runtime of the tests.

Gain in test time

Baseline: 1h11m47s (nightly 30/07 https://github.com/IntersectMBO/mithril/actions/runs/30506077425/job/90756011560)

After commit 1: 1h00m56s (https://github.com/IntersectMBO/mithril/actions/runs/30538872179/job/90858636858)

After commit 2: 40m50s (https://github.com/IntersectMBO/mithril/actions/runs/30552401815/job/90904114168?pr=3443)

Pre-submit checklist

• Branch
  • Tests are provided (if possible)
  • Crates versions are updated (if relevant)
  • CHANGELOG file is updated (if relevant)
  • Commit sequence broadly makes sense
  • Key commits have useful messages
• PR
  • All check jobs of the CI have succeeded
  • Self-reviewed the diff
  • Useful pull request description
  • Reviewer requested

Comments

Issue(s)

Closes #3433

[github-actions]

Test Results

     5 files  ±0     209 suites  ±0   1h 50m 10s ⏱️ - 1h 25m 2s
 3 411 tests +5   3 411 ✅ +5  0 💤 ±0  0 ❌ ±0 
11 180 runs  +5  11 180 ✅ +5  0 💤 ±0  0 ❌ ±0 

Results for commit 440fee2. ± Comparison against base commit bf1c9b3.

♻️ This comment has been updated with latest results.