Add instances for std Duration/SystemTime

[Fuuzetsu]

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[frol]

@Fuuzetsu Thank you for contributing to borsh! Unfortunately, we won’t merge this PR as date serialization is too opinionated, see previous discussion #131 (comment)

[Fuuzetsu]

I'm a bit confused... For Duration, the instances just serialise the individual fields as-is, no opinions. It's the same code as if we wrote derive(BorshSerialize, BorshDeserialize) inside stdlib... No opinions needed.

For SystemTime, this is the same implementation as in serde so at least there's a very big precedent.

Not being able to de/serialise stdlib types is very, very sad because it adds another hurdle to adding support in other crates that include Duration and such.

If someone does have an opinion on how to serialise a type then they should newtype it or use deserialize_with or something, right?

[frol]

@Fuuzetsu borsh is not Rust serialization format. There are other languages with their own defaults for internal implementation of "duration". See borsh specification here: https://borsh.io/, there is no sane default format for time.

For SystemTime, this is the same implementation as in serde so at least there's a very big precedent.

They regret it: serde-rs/serde#2108

Not being able to de/serialise stdlib types is very, very sad because it adds another hurdle to adding support in other crates that include Duration and such.

It is explicit and this is essential property for a schema-less binary format.

If someone does have an opinion on how to serialise a type then they should newtype it or use deserialize_with or something, right?

Exactly.