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/flappy_bird.lua

@@ -78,8 +78,8 @@ function draw()
         renderer.text(game.width() / 2 - 50, game.height() / 2, "Tap to Start", true)
     
     elseif state == STATE_PLAYING then
-        -- Draw bird
-        renderer.circle(20, game.vars.bird_y, BIRD_SIZE, true, true)
+        -- Draw bird (convert to integer)
+        renderer.circle(20, math.floor(game.vars.bird_y + 0.5), BIRD_SIZE, true, true)
         
         -- Draw pipes
         for i = 1, #game.vars.pipes do