chrono types support

[milesgranger]

Change Summary

This mainly adds ToTypesenseField support for chrono types, behind a feature gate of course. Additionally adds types that our project uses which wasn't covered already. ie Option<T> and Vec<Option<T>>.

Then one small fix in the derive macro to use ::serde::Serialize instead since I'm using this within another proc-macro.

PR Checklist

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[RoDmitry]

@milesgranger review my changes, and tell me if it's ready to merge.

[milesgranger]

I think that's a lot better, thanks for the help, @RoDmitry! :)

[RoDmitry]

Thank you! 🎉