Fix triggered Monster Tide spawn; fix Tower dungeon handoff

[longfruit]

Description

• Monster Tide spawn that depends on a trigger (like killing the first 20 mobs in Floor 1 Chamber 1 to trigger spawning the last 3) used to not trigger because its source ID was not kept, causing SceneScriptManager to fail to find its relevant triggers.
• After succeeding a Tower challenge, handoff (to Floor 1 Chamber 2 for example) was not happening because no DungeonManager was registered to the Tower scene, causing challenge completion event to be missed.

Issues fixed by this PR

Type of changes

• Bug fix
• New feature
• Enhancement
• Documentation

Checklist:

• My code follows the style guidelines of this project
• My pull request is unique and no other pull requests have been opened for these changes
• I have read the Contributing note and Code of conduct
• I am responsible for any copyright issues with my code if it occurs in the future.