Add textures to snake

We need 3 textures for the snake 🐍 :

- head, 1 segment, always visible
- body, many segments, visible after collecting the second pickup (after tail)
- tail, 1 segment, visible after collecting the first a pickup.

So:
- score = 0:

head

- score = 1:

head - tail

- score = 2:

head - body - tail

- score = 3:

head - body - body - tail

and so on

Should be easy to create in GIMP.

cc @H4wk507

The issue names no files, tests, or entry points. Start by locating the snake rendering and asset-loading code, then check how segment sprites are selected. Done means the snake displays head, tail, and body textures according to scores 0, 1, 2, and higher as described.

Written by the indexing model from the issue text.