Spawn a border around the world atlas for now

Also spawn the rover within a single chunk in the middle

pkg/game/atlas_test.go

@@ -134,3 +134,27 @@ func TestAtlas_Grown(t *testing.T) {
 	assert.NoError(t, err)
 	assert.Equal(t, Tile(3), tile)
 }
+
+func TestAtlas_SpawnAtlasBorder(t *testing.T) {
+	// Start with a small example
+	a := NewAtlas(2, 2)
+	assert.NotNil(t, a)
+	assert.Equal(t, 4, len(a.Chunks))
+
+	assert.NoError(t, a.SpawnAtlasBorder())
+	tile, err := a.GetTile(Vector{0, 0})
+	assert.NoError(t, err)
+	assert.Equal(t, TileEmpty, tile)
+
+	tile, err = a.GetTile(Vector{1, 1})
+	assert.NoError(t, err)
+	assert.Equal(t, TileWall, tile)
+
+	tile, err = a.GetTile(Vector{-1, -1})
+	assert.NoError(t, err)
+	assert.Equal(t, TileEmpty, tile)
+
+	tile, err = a.GetTile(Vector{-2, -2})
+	assert.NoError(t, err)
+	assert.Equal(t, TileWall, tile)
+}