bugfix: IndexOutOfRangeException in pathfinding due to byte overflow

[eduardosmaniotto]

Two IndexOutOfRangeException bugs caused by byte arithmetic overflow when
monsters walk near map edges, plus additional performance improvements on the
hot neighbor-expansion path.

Bug fixes

Bug 1: Byte loop counter overflow in ScopedGridNetwork.Prepare — maxX
is int (byte+byte promotes to int) but the loop used byte x. At offset 240
with segment length 16, maxX = 256. When x wraps from 255→0 the loop
continues, GetIndexOfPoint(0, y) returns -1, crashing on _gridNodes[-1].

Bug 2: Byte overflow in BaseGridNetwork.GetPossibleNextNodes direction
offsets — (byte)(node.X + (-1)) wraps to 255. The code accessed
grid[255, y] before the bounds check could reject it.

Additional fix in GetOffset — (byte)(gridSize - segmentLength) wraps
negative values to large positives (e.g. (byte)(-6) = 250), pushing the
segment outside grid bounds.

Performance improvements (same hot path)

• Unsigned range check — (uint)x > 255 replaces two signed comparisons
  with one branch per axis.
• Single grid read — grid[newX, newY] read once, reused for safezone
  check and cost mask, eliminating redundant byte[,] bounds checks.
• Flat direction arrays — two sbyte[] instead of sbyte[,], removing 2D
  stride multiply and improving JIT bounds-check elimination.
• Fixed latent cost bug — newG now uses the masked costToNode instead
  of raw this._grid[...], so safezone flags (bit 7) no longer corrupt path
  cost.

[gemini-code-assist]

Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses critical IndexOutOfRangeException bugs in the pathfinding system caused by byte arithmetic overflows. By switching loop counters to integers, enforcing stricter bounds checking, and sanitizing offset calculations, the changes ensure that pathfinding operations remain stable even when monsters move near the edges of the map.

Highlights

• Loop Counter Overflow Fix: Updated loop variables in ScopedGridNetwork from byte to int to prevent infinite loops caused by byte overflow when iterating near grid boundaries.
• Bounds Checking Improvement: Refactored BaseGridNetwork to perform bounds checking before accessing the grid array, preventing IndexOutOfRangeException during pathfinding.
• Offset Calculation Safety: Improved GetOffset logic by clamping values before casting to byte, ensuring segment offsets remain within valid grid bounds.

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[gemini-code-assist]

Code Review

This pull request introduces safety checks and fixes overflow bugs in the pathfinding grid networks. Specifically, it moves the bounds check in BaseGridNetwork to prevent out-of-bounds array access, changes loop counters from byte to int in ScopedGridNetwork to avoid infinite loops from overflow, and adds index validation. The reviewer noted that casting wrapped coordinates directly to byte in BaseGridNetwork can still cause logical bugs (like teleportation across the map edges) and suggested performing coordinate arithmetic using int before casting.

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