Report terrain validation trace diagnostics

[ogyrec-o]

Summary

Adds a non-breaking terrain interaction validation report API with server-authoritative ray trace diagnostics.

Why

frevenengine/freven-engine#386 rapid LMB smoke now has one remaining rare rollback after #120:

• FaceMismatch is gone.
• Most rapid break actions commit.
• A rare break can still be rejected with Occluded.

Occluded must not be blindly relaxed because it protects against breaking through another block. To diagnose correctly, runtime/server code needs to know which authoritative trace hit caused the rejection without duplicating DDA logic outside the shared validator.

What changed

• Adds TerrainInteractionTraceHitV2.
• Adds TerrainInteractionTraceV2.
• Adds TerrainInteractionValidationReportV2.
• Adds validate_terrain_interaction_v2_report(...).
• Keeps existing validate_terrain_interaction_v2(...) API source-compatible by delegating to the report API.
• Includes the authoritative trace hit block id, position, face, distance, and contact point.
• Adds regression coverage proving reports expose the occluding trace hit.

Boundaries

• no Vanilla source changes
• no engine source changes
• no Boot changes
• no protocol changes
• no validation behavior changes
• no server authority weakening
• no client prediction as authority

Validation

• cargo +stable fmt --all -- --check
• cargo +stable test --locked -p freven_block_api terrain_interaction
• cargo +stable test --locked --workspace
• cargo +stable clippy --locked --workspace --all-targets -- -D warnings
• git --no-pager diff --check

Related:

• frevenengine/freven-engine#386
• Allow break face drift for same target block #120
• Trace server terrain action terminal rejects freven-vanilla#90
• Use engine-presented terrain for block interaction freven-vanilla#89
• frevenengine/freven-engine#396