Simplify significant digits rounding and account for more cases.
Simplify significant digits rounding and account for more cases.

Instead of checking for special cases separately, the new rounding
mechanism checks for the number of current significant digits and
intended significant digits and removes a trailing '.0' or adds zeros,
based on the need.

Also accounts for floats in exponential notation (e.g. 1.23e-5) by
adapting the regular expression used.
This notation may occur in statistics values.

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