Festering Portal

Rebuilt for Minecraft 26.3.

• The corruption is a change of palette and nothing more: water near anything lava could light stays water, so a pond beside a house no longer burns the house down, and every swap keeps the old block's facing, half, flame and connections instead of resetting them.
• Crying obsidian counts as portal frame alongside obsidian.
• A config file without spreadIntervalTicks falls back to 60, the documented default, rather than 20.