Fix geometry deduplication in LOD child tiles

[Copilot]

The ProcessLodLevels method was calling GenerateTiles without passing the processedGeometries parameter, causing geometries already processed at parent LOD levels to be duplicated in child LOD tiles.

Changes

• Updated ProcessLodLevels signature to accept HashSet<string> processedGeometries parameter
• Pass processedGeometries through to GenerateTiles call for LOD children
• Updated both call sites (CreateTileForLargestGeometries and CreateTile) to pass their respective processed geometry sets

// Before
private void ProcessLodLevels(BoundingBox bbox, Tile tile, int lod, bool createGltf, bool keepProjection)
{
    var lodNextTiles = GenerateTiles(bbox, t2, new List<Tile>(), nextLod, createGltf, keepProjection);
}

// After
private void ProcessLodLevels(BoundingBox bbox, Tile tile, int lod, bool createGltf, bool keepProjection, HashSet<string> processedGeometries)
{
    var lodNextTiles = GenerateTiles(bbox, t2, new List<Tile>(), nextLod, createGltf, keepProjection, processedGeometries);
}

This ensures the size-based geometry prioritization correctly deduplicates across all LOD levels.

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