ConcurrentDictionary removed. Kernel made dependent on the shared GPU context.

PerfectNumbers.Core/Gpu/MersenneNumberIncrementalGpuTester.cs

@@ -16,7 +16,7 @@ public class MersenneNumberIncrementalGpuTester(GpuKernelType kernelType, bool u
     {
         throw new NotImplementedException($"GPU incremental scanning requires the device cycle heuristics implementation (kernel: {_kernelType}, GPU order: {_useGpuOrder}).");
 
-        var gpuLease = GpuKernelPool.GetKernel();
+        var gpuLease = GpuKernelPool.Rent();
         var accelerator = gpuLease.Accelerator;
         var stream = gpuLease.Stream;
         int batchSize = GpuConstants.ScanBatchSize; // large batch improves GPU occupancy