With some inputs larger than `BiggestUInt.high`, `parseBiggestUInt` proc
in `parseutils.nim` fails to detect overflow and returns random value.
This is because `rawParseUInt` try to detects overflow with `if prev >
res:` but it doesn't detects the overflow from multiplication.
It is possible that `x *= 10` causes overflow and resulting value is
larger than original value.
Here is example values larger than `BiggestUInt.high` but
`parseBiggestUInt` returns without detecting overflow:
```
22751622367522324480000000
41404969074137497600000000
20701551093035827200000000000000000
22546225502460313600000000000000000
204963831854661632000000000000000000
```
Following code search for values larger than `BiggestUInt.high` and
`parseBiggestUInt` cannot detect overflow:
```nim
import std/[strutils]
const
# Increase this to extend search range
NBits = 34'u
NBitsMax1 = 1'u shl NBits
NBitsMax = NBitsMax1 - 1'u
# Increase this when there are too many results and want to see only larger result.
MinMultiply10 = 14
var nfound = 0
for i in (NBitsMax div 10'u + 1'u) .. NBitsMax:
var
x = i
n10 = 0
for j in 0 ..< NBits:
let px = x
x = (x * 10'u) and NBitsMax
if x < px:
break
inc n10
if n10 >= MinMultiply10:
echo "i = ", i
echo "uint: ", (i shl (64'u - NBits)), '0'.repeat n10
inc nfound
if nfound > 15:
break
echo "found: ", nfound
```
