[SkyBlade1978]

Summary

Keep expansion machine data intact when older worlds are opened on Minecraft
1.21.11. The shared migration hook lets basePower preserve machine directions,
inventories and item wear before Minecraft converts the chunk or player data.
Companion callbacks now finish in either order, including restoration of saved
entities.

Base Metals keeps its existing registry names, recipes, materials and balance.
The patch version is 3.1.2.121111.

Checks

• Full build, Javadoc, dependency, archive, checksum and Eclipse audits pass;
  all 119 unit tests pass without skips.
• The player jar matches the one used for the combined basePower, baseSteam
  and baseElectric tests.
• Original Advantage and released base* world upgrades, both migration-hook
  orders, full restarts and two 30-minute endurance worlds pass their checks.
• The matching three-mod client has also passed manual testing.

This patch is being released first so the expansions can use a public,
reproducible dependency rather than a local-only build.