Icarus hotfix 3.0.21.155335 fixes prebuilt-structure missions

Icarus has received hotfix 3.0.21.155335-rel-DangerousHorizons, aimed at missions that use prebuilt structures.

The patch fixes multiple cases where those structures failed to spawn, which previously prevented missions from starting. It also fixes cases where prebuilt structures were not cleaned up after mission completion, with cleanup still respecting server settings.

Name collisions between prebuilt structures from different missions, which could block new structures from spawning when they should have, are also resolved.

One note for existing runs: some missions may spawn duplicate structures once as a result of the change. The patch says this should be a one-off, as prebuilt structures are now tracked more closely and references persist as they did not before.