The spec asks us to serialize with no more than 6 decimal digits, so if
the number is smaller than 0.000,000,5 then it can't produce any digits
and we should serialize it as 0, instead of using scientific notation.
We also shouldn't use scientific notation for very large numbers, but we
don't seem to have a flag to disable that in the formatter, so I'm
leaving a FIXME for now.
Improves some test results. 🎉
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