Calculates the arithmetic mean (average) of a list.
與 .wl 參考的差異： `Mean`, `Quantile` and `RootMeanSquare` of an `EventSeries` or `TemporalData`
Mean[data]
Mean[dist]
Mean[{1, 2, 3, 4, 5}]
→ 3Mean[{10, 20, 30}]
→ 20Mean[{1, 2, 3}]
→ 2Mean[{5}]
→ 5Mean[{-5, 5}]
→ 0Mean[{1.5, 2.5, 3.5}]
→ 2.5Mean[{0, 0, 0, 10}]
→ 5/2Mean[{-10, -5, 0, 5, 10}]
→ 0