Add CoreModeIceTileOverlay map metadata property

[SilverDorian46]

this is an effect specific to vanilla Core, which has been unusable in custom maps (without writing a code mod) until now.
if enabled, an ice graphic will be overlaid on the surface of Solid Tiles when the Core Mode is Cold.
may be useful for maps looking to emulate vanilla Core

[maddie480-bot]

The pull request was approved and entered the 3-day last-call window.
If no further reviews happen, it will end on Apr 19, 2026, 7:42 AM UTC, after which the pull request will be able to be merged.

[microlith57]

one last approving review, for fun

[maddie480-bot]

The pull request was approved and entered the 3-day last-call window.
If no further reviews happen, it will end on Apr 19, 2026, 11:20 AM UTC, after which the pull request will be able to be merged.

[maddie480-bot]

The last-call window for this pull request ended. It can now be merged if no blockers were brought up.

[maddie480]

I said "update with rebase", thanks GitHub (since the history vanished: I hit "update branch" to run the tests one last time before merging, and that dum dum made a merge commit instead)

[maddie480]

Rebased and squashed manually, no change made: https://github.com/EverestAPI/Everest/compare/b1ac854d468e419ccb49a85d62d1ca83b34a813f..06465b9b24fdf3338e4cdfe0706472c2e633cd05