[002] Snake

var _my_source: TileSetAtlasSource = tile_set.get_source(0) as TileSetAtlasSource
var _tile_id: int = _my_source.create_alternative_tile(Vector2i.ZERO)
var _tile_data: TileData = _my_source.get_tile_data(Vector2i.ZERO, _tile_id)

only change the head and tail of the snake
keep track of each snake tiles
keep track of tail index (start at 0)
on each step
    track old tail index
    track old head index [tail_index - 1]
    track new head index = old head_index + direction
        on move
            old tail index in array = new head
            remove old tail tile
            add new head tile
            tail_index += 1
            if tail_index == snake_array.size():
                tail_index = 0

lerp_step = 1.0 / snake size
lerp_curr = lerp_step
var index: int = tail_index
for i in snake_size:
    tile_data[index].modulate = TAIL_COLOR.lerp(HEAD_COLOR, lerp_curr)
    lerp_curr += lerp_step
    
    index += 1
    if index == snake_size:
        index = 0