Add basic Unreal Engine 5.7 compatibility

[Gravitonator]

Tested on UE 5.7.

Changes:

• Updated EngineVersion to 5.7.0
• Initialized Construction System struct defaults to remove UE 5.7 log errors

Verified:

• Plugin compiles successfully
• Demo map loads
• PrefabRandomizer works as expected

[Gravitonator]

I pushed one more fix into this PR for a PrefabRandomizer crash on UE 5.7.

Commit:
61cd46b — Fix PrefabRandomizer crash by deferring randomization to next tick

This changes the direct Randomize(Seed) call in BeginPlay() to a next-tick call via the timer manager, with a validity check before execution. That seems to avoid the crash caused by running the randomization too early.

Please test it on your side as well and let me know if it fixes the issue.