previously when T was smaller than 8 bits, it was possible for base
to overflow T (because base is a u8). this patch prevents this by
accumulating into a U rather than T which is at least 8 bits wide.
this is the best way i could think of to maintain performance. this
will only affect parsing of integers less than 8 bits by adding one
additional cast at return. additionally, this patch may be slightly
slower to return an error for integers less than 8 bits which overflow
because it will accumulate a few more digits before the overflow check
at return.
* add tests which previously overflowed when they shouldn't have
closes#18157
5bbacb0c8c