Allow sculk to spread onto any non-air block

[TheyCallMeFatbird]

Motivation

• Make sculk spreading allow placement on any block type except air so spread can cover chests, beds, bedrock, full blocks, etc.

Description

• Add SculkSpreadManagerCursorMixin that injects into canSpreadTo(WorldAccess, BlockPos) and forces the check to return !world.getBlockState(pos).isAir().
• Register the new mixin in src/main/resources/tutorialmod.mixins.json by adding SculkSpreadManagerCursorMixin to the mixin list.
• Changes are limited to src/main/java/net/tcmfatbird/tutorialmod/mixin/SculkSpreadManagerCursorMixin.java and the mixin configuration file.

Testing

• Attempted to run ./gradlew genSources to generate sources and validate, but Gradle downloads failed due to network/proxy restrictions (HTTP 403), so no automated build or runtime tests were executed.
• No automated tests were run in this environment; changes are limited and should be validated with a full build and in-game testing locally.

---

Codex Task