feat: narrow return type for `min()`, `max()`, `median()` and `mean()`

[simPod]

Consider whether the input is empty or not

[coveralls]

Pull Request Test Coverage Report for Build 8580273017

Details

• 1 of 1 (100.0%) changed or added relevant line in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 98.781%

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Totals
Change from base Build 8571532296:	0.0%
Covered Lines:	4377
Relevant Lines:	4431

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💛 - Coveralls

[azjezz]

Thank you @simPod 🙏