Use LastDigit enum across Mersenne scanners

PerfectNumbers.Core/Gpu/MersenneNumberIncrementalGpuTester.cs

@@ -12,7 +12,7 @@ public class MersenneNumberIncrementalGpuTester(GpuKernelType kernelType, bool u
     private readonly GpuKernelType _kernelType = kernelType;
     private readonly bool _useGpuOrder = useGpuOrder;
 
-    public void Scan(ulong exponent, UInt128 twoP, bool lastIsSeven, UInt128 maxK, ref bool isPrime)
+    public void Scan(ulong exponent, UInt128 twoP, LastDigit lastDigit, UInt128 maxK, ref bool isPrime)
     {
         throw new NotImplementedException($"GPU incremental scanning requires the device cycle heuristics implementation (kernel: {_kernelType}, GPU order: {_useGpuOrder}).");
 
@@ -23,7 +23,7 @@ public class MersenneNumberIncrementalGpuTester(GpuKernelType kernelType, bool u
         int batchSize = GpuConstants.ScanBatchSize; // large batch improves GPU occupancy
         UInt128 kStart = 1UL;
         ulong divMul = (ulong)((((UInt128)1 << 64) - UInt128.One) / exponent) + 1UL;
-        byte last = lastIsSeven ? (byte)1 : (byte)0; // ILGPU kernels do not support bool parameters
+        byte last = lastDigit == LastDigit.Seven ? (byte)1 : (byte)0; // ILGPU kernels do not support bool parameters
 
         var pow2Kernel = gpuLease.Pow2ModKernel;
         var incKernel = gpuLease.IncrementalKernel;