`boost::charconv::detail::parser` is not made for parsing (large)
integers in exponential notation.
It is mainly tested for parsing floating point numbers in hexadecimal format.
Given we know ICU will output either an integer string or a number in
"E notation" (1.2E2) we can convert that rather easily to a "regular"
integer string by "moving" the dot to the right according to the
exponent. The trailing gap is filled with zeros before passing it to
`from_chars` which is now able to handle the range checks for us.
This avoids overflows that can happen when multiplying the
significant by the exponent which, due to integer arithmetic, would be
cumbersome to guard against.
Any situation that could yield a fractional or a too large value can be caught early.
