Write fractal terrain gen seeds instead of reading them

ArcTerrainGen.save_binary called read_dword for the two seeds, so
packing a Peaked, Ridged, Rolling or Mesa terrain gen raised TypeError.
The sample cache only has Planar and Targa terrain gens.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

mbEditorPro2.0/arcane/zones/ArcTerrainGen.py

@@ -57,8 +57,8 @@ class ArcTerrainGen:
             stream.write_dword(self.terrain_octaves)
             stream.write_float(self.terrain_offset)
             stream.write_float(self.terrain_gain)
-            stream.read_dword(self.terrain_seeds[0])
-            stream.read_dword(self.terrain_seeds[1])
+            stream.write_dword(self.terrain_seeds[0])
+            stream.write_dword(self.terrain_seeds[1])
         if self.terrain_type == 4:
             stream.write_float(self.terrain_max_x)
             stream.write_float(self.terrain_max_z)