correct handling of floats with N digits (~f and ~Nf)

correct handling of floats with N digits (~f and ~Nf)

This addresses #2771. Many thanks to @tmerr for reporting the issue!

The code was posted by @UWN in:

    https://github.com/mthom/scryer-prolog/discussions/2805

Many thanks! With additional inputs by @adri326 and @notoria, who also
posted interesting approaches which could help to increase precision
in cases that are currently not ideally handled. Thank you all!

Please see the issue and discussion for more information.