[pandas 2.0] Re-factor of the DataType classes

[joshuastorck]

• Changing PrimitiveType to NumericType
• Removing the macro for declaring sub-types of NumericType and instead using template arguments
• Addding a static SINGLETON member to the NumericType base class instead of the macros for methods for creating singletons for each numeric type
• Removing NullType's inheritance of PrimitiveType
• Removing intermediate base class between {Integer,Floating}ArrayImpl and PrimitiveType and just making a concrete template based class {Integer,Floating}Array
• Changing FLOAT and DOUBLE to FLOAT32 and FLOAT64

[wesm]

Cool, this looks good -- thanks for making the Cython code compile again! I wasn't aware of the trailing return type syntax in C++11, so that's super helpful.