fix: security fix for integer truncation in arena memory copies

[myarichuk]

🎯 What: An integer overflow/truncation vulnerability existed where memory allocations and copies exceeding 32-bit uint limits (4GB) could be silently truncated due to casts.
⚠️ Risk: Memory size variables that exceeded uint.MaxValue were vulnerable to truncation when passed into unmanaged copies, leading to out-of-bounds reads/writes, application crashes, or severe memory corruption since the intended copy sizes would shrink down to small incorrect values.
🛡️ Solution: Implemented explicit 64-bit bounds checks > uint.MaxValue directly after ulong size calculations in ArenaList.cs and ArenaPtrStack.cs to defensively throw new InvalidOperationException() rather than silently truncating or overwriting unmanaged buffers.

Also ensured zero-extension casting (ulong)(uint) is preserved to properly guard against negative integers sign-extending into unintended bounds-bypassing values.

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PR created automatically by Jules for task 8033739845305995073 started by @myarichuk

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