fix: prevent double-plant half duplication

[twme-ai]

Summary

• stop exposing the half property for multi-block Bisected block data by default
• preserve valid single-block half editing for stairs and trapdoors
• add BlockDataFilter.AllowUnsafeBisectedData for servers that intentionally need the original behavior
• add regression coverage for the default and opt-in behavior

Root cause

DebugStickPro applies block data to only the targeted block with physics disabled. Changing a double plant from its upper half to a lower half can therefore leave two independent lower halves, each of which produces a drop when broken.

The existing configurable blacklist can mitigate this only when explicitly enabled. The shared separation point now protects classic and copy modes by default. Administrators can set BlockDataFilter.AllowUnsafeBisectedData: true to restore multi-block Bisected editing when that risk is acceptable. Stairs and trapdoors remain available because their half property is a valid single-block placement property.

Adding the setting increments the config version to 8, following the project's existing config migration behavior.

Verification

• mvn -B test (4 tests, 0 failures)
• mvn -B package
• GitHub Actions build

Fixes #37