Gate overworld buttons on the completed step (#286)

OverworldLoop (home/overworld.asm) jumps straight to .moveAhead while
wWalkCounter is nonzero: JoypadOverworld -- the START check, the A
check, and direction initiation -- only ever runs while the player
stands on a tile, and a button pressed mid-step is simply never seen.
The port ran handleInput() every frame regardless, so a mid-step
A/START pushed its TextBox/StartMenu right there and froze Red between
tiles, mid-animation (the Nurse Joy run-up in the report).

Gate handleInput on player.moving like the original.  The port-invented
wall-bonk SFX cooldown is hoisted above the gate so it keeps ticking on
held-direction frames mid-step exactly as before.

Adds tests/parity_midstep_buttons.lua: mid-step and last-frame A/START
presses are swallowed and the step completes, and both buttons work
again once the player stands on the tile.

src/world/OverworldController.lua

@@ -938,6 +938,24 @@ end
 function OverworldState:handleInput()
   local input = Game.input
 
+  -- the wall-bonk SFX cooldown ticks with any held direction, step or not
+  -- (it is a port invention, not part of JoypadOverworld, so the
+  -- wWalkCounter gate below must not freeze it mid-step)
+  if self:dirHeld() then
+    self.bumpCooldown = math.max(0, (self.bumpCooldown or 0) - 1)
+  end
+
+  -- OverworldLoop (home/overworld.asm) gates ALL of JoypadOverworld on
+  -- wWalkCounter == 0 ("if the player sprite has not yet completed the
+  -- walking animation" it jumps straight to .moveAhead): A, START and
+  -- direction initiation are only ever looked at while the player stands
+  -- on a tile, and a button pressed mid-step is simply never seen.
+  -- Without this gate a mid-step A/START pushed its TextBox/StartMenu
+  -- right there and froze Red between tiles, mid-animation (#286).  Held
+  -- directions need no buffering -- isDown below picks them up on the
+  -- landing frame.
+  if self.player.moving then return end
+
   if input:wasPressed("a") then
     self:interact()
     return
@@ -974,7 +992,6 @@ function OverworldState:handleInput()
           self.bumpCooldown = 16
         end
       end
-      self.bumpCooldown = math.max(0, (self.bumpCooldown or 0) - 1)
       return result
     end
   end