Support Complex and BigDecimal for Date#{+,-}

[ksss]

Date#{+,-} allows to pass an object with numeric argument and to_r method.

https://github.com/ruby/ruby/blob/6d540c1b9844a5832846618b53ce35d12d64deac/ext/date/date_core.c#L5785-L5786

For example, Complex and BigDecimal can be passed.

Date.today + Complex(1, 0)
#=> Date

Date.today + BigDecimal("1")
#=> Date

To achieve this behavior, the _ToR interface was introduced.

And Integer, Rational, and even Float are removed because they satisfy the condition of (Numeric & _ToR).

[soutaro]

Interesting! 👏 👏