Count significant figures in a number and optionally round to N significant figures. Accepts the number as a string to preserve trailing zeros (e.g. '1.200' has 4 sig figs). Applies standard sig fig rules: leading zeros do not count, trailing zeros after a decimal point count, trailing zeros before a decimal point are treated as significant. Also returns the number in scientific notation. Essential for laboratory measurements, error analysis, and maintaining proper precision in chained calculations.