Change parameter of `try_pack` from `T` to `&T`

[ik1ne]

Any::try_pack takes message: T as parameter, consuming it. However, taking message: &T instead of message: T would work too, allowing the callers to reuse message.

[fdeantoni]

Good point. Let me check if this can simply be added as well.

[Sushisource]

Same for unpack. A common pattern would be to try to unpack as a series of different types, but taking self by ownership prevents this and forces you to explicitly check the type url first.

AFAICT it's a trivial change, since self never actually needs to get consumed in the unpacking functions.