feat: Add GeoSeries.area

[arwas11]

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Fixes #308738592 🦕

[tswast]

mypy error: "Series" not callable [operator]

Note: since .area is a "property", we don't call it as a function. We pretend it's just a normal attribute.

Suggested change

	bf_series.area()
	bf_series.area

A bit more about properties: https://www.pythonmorsels.com/making-read-only-attribute/ and https://realpython.com/python-property/

It's very similar to what Java calls "getter" and "setter" functions, but in this case Python allows it to look like a normal attribute.