Run progress callback checks less frequently in the main VDBE evaluation

loop.  This makes up for the extra CPU cycles used to increment the cycle
counter for SQLITE_STMTSTATUS_VM_STEP.

FossilOrigin-Name: 3e8b02011db2f393d4850115a471709b0a88594f

test/progress.test

@@ -166,7 +166,7 @@ do_test progress-1.7 {
   set ::res [list]
   db eval {SELECT a, b, c FROM abc} {
     lappend ::res $a $b $c
-    db progress 10 "expr 1"
+    db progress 5 "expr 1"
     catch {db eval {SELECT a, b, c FROM abc} { }} msg
     lappend ::res $msg
   }