Scripts/Gundrak: Properly handle wipes on Drakkari Colossus encounter

[Odyssey]

Changes proposed:

Rework encounter evade logic so that

• If a wipe happens during a colossus stage, the colossus resets properly
• If a wipe happens during an elemental stage, the elemental resets and the colossus remains as is until re-merging/death.

Issues addressed:

Closes #27811

Tests performed:

builds; tested and working in-game