Add draw_shape and draw_shapes with tests

draw_shape turns 360 divided by the number of sides after each side and rejects
fewer than 3 sides. draw_shapes draws a triangle up to a decagon, each in a color
from the palette.

Task: MIL-003#3
Task: MIL-003#4
Task: MIL-003#5

src/turtle_challenges/constants.py

@@ -20,6 +20,9 @@ COLOR_CHANNEL_MIN = 0
 ## Largest value of one color channel.
 COLOR_CHANNEL_MAX = COLOR_MODE
 
+## Degrees in a full turn.
+FULL_TURN_DEGREES = 360
+
 ## Degrees in a right angle.
 RIGHT_ANGLE_DEGREES = 90
 
@@ -38,6 +41,15 @@ DASH_LENGTH = 10
 ## Challenge 2: length of the gap after each dash, in turtle units.
 GAP_LENGTH = 10
 
+## Challenge 3: fewest sides of a polygon (a triangle).
+MIN_POLYGON_SIDES = 3
+
+## Challenge 3: most sides of a polygon drawn in a row (a decagon).
+MAX_POLYGON_SIDES = 10
+
+## Challenge 3: length of one side of a polygon, in turtle units.
+POLYGON_SIDE_LENGTH = 100
+
 ## Challenge 3: named colors a polygon is drawn in.
 COLOR_PALETTE: tuple[str, ...] = (
     "CornflowerBlue",