Fix Lua game float-to-int conversion errors for renderer.circle()

All games had the same issue: renderer.circle() requires integer arguments,
but float calculations produced non-integer coordinates.

Fixed in all games using math.floor(x + 0.5) for proper rounding:
- pong.lua: Ball position
- air_hockey.lua: Puck position
- asteroids.lua: Asteroid positions
- ball.lua: Ball and trail positions, velocity line
- breakout.lua: Ball position
- flappy_bird.lua: Bird Y position
- counter.lua: Last touch marker position
- snake.lua: Food position (center calculation)
- tic_tac_toe.lua: O circle center position

Also fixed floating-point coordinate calculations in ball and line
drawing to ensure all coordinates are integers.

games/lua_examples/snake.lua

@@ -127,9 +127,9 @@ function draw()
             renderer.rect(seg.x * CELL_SIZE, seg.y * CELL_SIZE, CELL_SIZE, CELL_SIZE, true, filled)
         end
         
-        -- Draw food
-        renderer.circle(game.vars.food_x * CELL_SIZE + CELL_SIZE / 2, 
-                       game.vars.food_y * CELL_SIZE + CELL_SIZE / 2, 
+        -- Draw food (convert center to integers)
+        renderer.circle(math.floor(game.vars.food_x * CELL_SIZE + CELL_SIZE / 2 + 0.5), 
+                       math.floor(game.vars.food_y * CELL_SIZE + CELL_SIZE / 2 + 0.5), 
                        CELL_SIZE / 2, true, true)
         
         -- Draw score