Fix boss spawn bitmap conflict at (25,25)

[0x1NotMe]

Summary

• Fixed InvalidLocationBitmap(2, 2) error when moving to boss location (25,25)
• Updated combat test to accept both survival and death as valid outcomes

Problem

When a player occupies index 1 and attempts to move to location (25,25), the game would revert with InvalidLocationBitmap(2, 2). This happened because the boss spawn logic only checked the monster bitmap, not the player bitmap, before attempting to spawn a boss at the reserved index.

Solution

Modified _checkForAggro in Instances.sol to check both player and monster bitmaps before attempting boss spawn. If a player occupies the boss index, the function now returns (0, false) instead of attempting to spawn and reverting.

Changes

1. Instances.sol: Added combined bitmap check for boss spawn logic
2. BattleNadsCombatTest.t.sol: Fixed flaky test that was incorrectly asserting characters must survive combat

Testing

• Added testBitmapLogic() to verify the fix logic
• All existing tests pass
• Combat test no longer flaky - correctly handles both survival and death outcomes

Gas Impact

Minimal - adds one additional bitmap check only for boss spawn scenarios at specific coordinates.

[thogard785]

While the description of the problem's solution is innaccurate, this does fix the bug.

The previous version was erroneously checking monsterBitmap & RESERVED_BOSS_INDEX. In your version, you check monsterBitmap & (1<<RESERVED_BOSS_INDEX). I believe this is the solution - the addition of the player bitmap is irrelevant.

Will merge this to also update the test.