Add non-finite float support to `facet-value`

[sydduckworth]

Currently deserializing to facet_value::Value fails if the input contains a non-finite (NaN, infinity, etc) float value.
This makes sense for JSON since it doesn't allow non-finite floats, but other formats like YAML do allow them.

My goal is to use facet-value to do partial tree extraction while parsing YAML files, but I'm currently blocked because the input files need to support NaN/Inf values.

I'd be happy to submit a PR making the change, but obviously that may be undesired from the JSON side.

[sydduckworth]

The simplest solution would be to just update VNumber::from_f64 to remove the is_finite() check. Any non-finite values would still be caught by the JSON serializer so there's no risk of emitting invalid JSON, but that would mean that facet_value::Value itself would no longer be guaranteed to be valid JSON.

[fasterthanlime]

The simplest solution would be to just update VNumber::from_f64 to remove the is_finite() check.

SGTM, I'll accept a PR doing that