refactor(M03): extract terrain chunk LOD planner

src/render/terrain/terrain_chunk_lod_policy.gd

@@ -0,0 +1,45 @@
+class_name TerrainChunkLodPolicy
+extends RefCounted
+
+## Immutable snapshot of the streamer's chunk-terrain LOD configuration.
+
+var is_enabled: bool:
+	get:
+		return _is_enabled
+
+var lod0_radius_chunks: int:
+	get:
+		return _lod0_radius_chunks
+
+var lod1_radius_chunks: int:
+	get:
+		return _lod1_radius_chunks
+
+var lod2_radius_chunks: int:
+	get:
+		return _lod2_radius_chunks
+
+var chunk_size_units: float:
+	get:
+		return _chunk_size_units
+
+var _is_enabled: bool
+var _lod0_radius_chunks: int
+var _lod1_radius_chunks: int
+var _lod2_radius_chunks: int
+var _chunk_size_units: float
+
+
+## Captures one renderer configuration snapshot for a deterministic plan.
+func _init(
+		is_enabled_value: bool,
+		lod0_radius_chunks_value: int,
+		lod1_radius_chunks_value: int,
+		lod2_radius_chunks_value: int,
+		chunk_size_units_value: float
+) -> void:
+	_is_enabled = is_enabled_value
+	_lod0_radius_chunks = lod0_radius_chunks_value
+	_lod1_radius_chunks = lod1_radius_chunks_value
+	_lod2_radius_chunks = lod2_radius_chunks_value
+	_chunk_size_units = chunk_size_units_value