Replace small-modulo uses with optimized helpers

PerfectNumbers.Core/Cpu/MersenneNumberResidueCpuTester.cs

@@ -21,7 +21,7 @@ public class MersenneNumberResidueCpuTester
 		q.Mod10_8_5_3(out ulong r10, out ulong r8, out ulong r5, out ulong r3);
 		// Step residues for q += 2*p
 		twoP.Mod10_8_5_3(out ulong step10, out ulong step8, out ulong step5, out ulong step3);
-                step10 %= 10UL;
+                step10 = step10.Mod10();
 
 		// Allowed last-digit sets for q depending on last digit of M_p
 		// lastIsSeven == true  => allow {7,9}