[LCI] Implement The Skullspore Nexus

[Susucre]

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[github-actions]

The Skullspore Nexus - (Gatherer) (Scryfall) (EDHREC)

{6}{G}{G}
Legendary Artifact
This spell costs {X} less to cast, where X is the greatest power among creatures you control.
Whenever one or more nontoken creatures you control die, create a green Fungus Dinosaur creature token with base power and toughness each equal to the total power of those creatures.
{2}, {T}: Double target creature's power until end of turn.

[Susucre]

Arf, I just realized that The Great Henge was set this way to work properly when you cast it but are not the owner (e.g. with Gonti, Lord of Luxury).

I'll reverse that change and do the same for the Nexus. Also adding tests on that, as apparently we have none. See #11166 for more on that.

[Susucre]

And I forgot to push the fix+test on that before merging. It is at #11330 if you want to give it a look (reverted modifications for Great Henge, did a similar change to nexus, and added a test for the future rework of those effects that got their counts confused).