[Expedition] Migrate to monorepo

[Gnuxie]

Present value

• Much better contributor onboarding if all packages are in one repository
  • Workflow is currently strange for editing MPS and Draupnir together.
• dependency management and maintenance simplified

Resources

Focus sessions: 20
NLnet goal: https://marewolf.me/posts/draupnir/24-nlnet-goals.html#goal-long-term-improvements-to-maintenance

[Gnuxie]

As of 2026-03-19 we have exhausted the focus session budget. We will add 5 more given that we had to take on some of the work of #96. We're at the closing stages now anyway.