[Proposal] Reduce CI time to max ~15 min. per run

[vicsn]

💥 Proposal

Now that we know which tests take the most amount of time, we can aim to:

• reduce compile time
• change or refactor some of the tests
  • removing the synthesizer job will require some discussion: [Proposal] Prune synthesizer CI job #2979
  • perhaps we can turn off proof generation to speed up testing