fix: allow NaNs

[jdbdnz]

Overview

MongoDB allows storing NaN in a double field. Mongoose Double does not.

Change

• change Mongoose Double and allow NaNs.

Testing

• wrote a test to ensure explicit NaN values save
• wrote a test to ensure implicit NaN values do not save

Feedback

Anything

[jdbdnz]

Meant to open this against my fork. Oops.