Add WorldGen determinism tests

[MichaelFisher1997]

Parent Issue

Part of #26 (Full Codebase Audit v3)

Category

Testing & Validation (1 day)

Problem

WorldGen should produce identical output for the same seed, but this isn't verified by tests.

Current State

• Basic noise tests exist (added in Add comprehensive unit tests and documentation (#19) #25)
• No full WorldGen determinism tests
• No golden output verification

Proposed Tests

test "WorldGen same seed produces identical chunks" {
    const gen1 = TerrainGenerator.init(12345, allocator);
    const gen2 = TerrainGenerator.init(12345, allocator);
    
    var chunk1 = Chunk.init(0, 0);
    var chunk2 = Chunk.init(0, 0);
    
    gen1.generate(&chunk1, null);
    gen2.generate(&chunk2, null);
    
    // Compare block data
    try testing.expectEqualSlices(BlockType, &chunk1.blocks, &chunk2.blocks);
}

test "WorldGen different seeds produce different chunks" {
    // ...
}

test "WorldGen golden output for known seed" {
    // Compare against saved expected output
}

Files to Create

• src/tests/worldgen_determinism.zig or add to src/tests.zig

Risk

None - pure test addition

Acceptance Criteria

• Determinism test: same seed → same output
• Different seed test: different seeds → different output
• Optional: golden output test for regression detection

[MichaelFisher1997]

/oc can you solve this issue

[opencode-agent]

Created PR #79

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