Add standard block shape vocabulary

[ogyrec-o]

Summary

Adds SDK-level public vocabulary for canonical block shape semantics.

This introduces reusable types for:

• block-local normalized shape boxes;
• canonical block shape faces;
• per-side occlusion masks;
• per-side side-solid/support masks;
• collision boxes;
• selection boxes;
• shape validation errors.

The vocabulary is re-exported through freven_world_guest_sdk alongside the existing block descriptor vocabulary.

Why

freven-engine#321 added the first engine-side canonical shape foundation, but long-term shape/collision/selection semantics should not remain engine-private.

The SDK needs shared vocabulary that can be consumed by engine runtime, game-owned authoring profiles such as freven.vanilla:blocktypes_v1, world/avatar APIs, and mod-facing tooling.

Details

• Adds BlockShapeFace.
• Adds BlockShapeBox.
• Adds BlockShapeSideMask.
• Adds BlockShapeDescriptor.
• Adds BlockShapeValidationError.
• Supports full cube, half block, and multi-box shapes.
• Keeps render mesh identity separate from collision/selection/query shape data.
• Keeps renderer/runtime ids out of public shape vocabulary.
• Re-exports the new vocabulary from freven_world_guest_sdk.

Validation

• cargo +stable fmt --all -- --check
• cargo +stable test --locked -p freven_block_sdk_types -p freven_world_guest_sdk
• cargo +stable clippy --locked -p freven_block_sdk_types -p freven_world_guest_sdk --all-targets -- -D warnings

Closes #113.