Increase handling of JSON Number large numbers (vs. string)

[peterbroadhurst]

Builds on #76 to cover some additional important cases where consumers of this library use types that need to support:

• Scientific notation in JSON structure
• The possibility of JSON Number encoded (vs. string) large numbers

The code does cause errors in some previously ignored scenarios that would result in bad numbers:

• Attempting to parse a HexUint64 from a number larger than 18446744073709551615
• Attempting to parse a HexUint64 from a fractional number like 1.2345

[EnriqueL8]

Looks good but spotted a problem

[matthew1001]

Thanks for covering these cases that I didn't in the original PR @peterbroadhurst. They look good to me with the exception of @EnriqueL8 's comment. I'll leave him to approve it once that comment has been resolved.

[EnriqueL8]

Looks good