Features:
- GPU Atomic Operations: AtomicAdd, AtomicSub, AtomicExchange, AtomicCompareExchange
- Extended Atomics: AtomicMin, AtomicMax, AtomicAnd, AtomicOr, AtomicXor
- Memory Ordering: AtomicLoad, AtomicStore with MemoryOrder enum
- Thread Fences: ThreadFence(MemoryScope) for synchronization
- Cross-backend compilation to CUDA, OpenCL, Metal, CPU

Quality Improvements:
- Zero warnings build (49 warnings resolved)
- Fixed CA1815, CA1307, CA2201, CA2213, CA1829, CA1849, CA1859 warnings

Dependency Updates:
- NuGet.Frameworks: 6.14.0 → 7.0.1
- MemoryPack: 1.21.1 → 1.21.4
- Microsoft.CodeAnalysis.CSharp: 4.14.0 → 5.0.0
- Microsoft.Extensions.*: Aligned to 9.0.10