RFC: extend allow_nan parameter to all number fields

Decimal field has an allow_nan parameter (False by default):

If True, NaN, Infinity and -Infinity are allowed, even though they are illegal according to the JSON specification.

Any objection to extend it to all numbers?

Currently, Int will reject those as they are not integers, but they pass Float which just pawned me.

Should we add the same validation in Float? Move it up to Number?

Even if it is useless for Int, I’d be tempted to extend it to Number.

• Those are special values with a special meaning so a different error message makes sense.
• Any Number subclass would inherit it -> less duplication.

This is a breaking change as the default would be False so Float would need to be explicitly passed allow_none=True.

[lafrech]

On second thought, from a practical perspective, modifying only Float is easier…

And an Int with allow_nan=True wouldn’t make sense.

Definitely better to do that on a per-field basis.

Shall I shoot a PR for Float?

[lafrech]

Implementation proposed in #945.

Breaking because default is False and because the signature of the field’s __init__ changes.