fix: auto-shift model coordinates to stay within Minecraft bounds (-16 to 32)

[wiflow]

Summary

When BetterModel exports models to Minecraft JSON format, element coordinates can exceed Minecraft's hard bounds (-16 to 32), causing errors like:

java.lang.IllegalArgumentException: Value at Z axis (-20.0) is out of bounds

This happens when the original bbmodel has coordinates slightly outside bounds, or when the split/export process applies offsets that push coordinates out of range.

Solution

This PR adds automatic bounds validation and coordinate shifting:

• Pre-calculates the bounding box of all cubes before JSON export
• Computes an offset to shift coordinates within valid bounds (-16 to 32)
• Applies uniformly to from, to, and rotation origin to keep model parts aligned

Example

A model part with Z range -20 to +9:

• Detects minZ = -20 is below -16
• Calculates offsetZ = +4
• Result: Z range -16 to +13 (within bounds)

Changes

• Added MIN_BOUND and MAX_BOUND constants
• Added calculateFrom() and calculateTo() helper methods
• Added calculateBoundsOffset() to compute required shift
• Modified Group.buildJson() to pre-calculate bounds and offset
• Modified Cube.buildJson() to accept and apply the offset

Testing

• Tested with models that have coordinates outside the -16 to 32 range
• Build compiles successfully
• Coordinates are shifted uniformly, preserving model alignment