Person properties cannot be of type float

[ChiragKumar9]

Currently, the values associated with person properties must implement Hash (in addition to a series of other traits):

ixa/src/people.rs

Line 397 in 8ae6321

type Value: Copy + Debug + PartialEq + Hash;

This means that person properties cannot be a float because f32/f64 do not implement Hash in Rust. Since wanting to store floats as person properties comes up a reasonable amount of times (i.e., time of last infection, natural history parameters potentially, maybe even per-person vaccine efficacy, etc.), we should have some general solution to this problem.

Here are two thoughts:

1. Declare whether the property will be indexed when defining the person property and accordingly require whether Hash be implemented on the type. Could also automatically call context.index_property(property) for such properties. Naturally enforces that float properties cannot be indexed, which feels like a good choice.
2. Internally store floats as some other type for which Hash is implemented. I can't really ever think of a case where our floats would be Nan, so potentially store floats as ordered_float::NotNan<f64> from crate ordered_float.

I think both solutions have their pros and cons, and I'm not yet sure which I prefer.

Side note: when making a person property that is a custom type, I have to derive a series of traits for the struct -- Debug, Clone, Copy, PartialEq, etc. Would it be possible to just do something like #[derive(IxaPersonProperty)]/is this a good idea, or would it be hiding important things from the user?

[ChiragKumar9]

Discussed IRL: we will use ordered_float. Whether this gets re-exported from ixa or not or ixa creates a new type called IxaFloat remains to be seen.