tonic-prost 0.14: ProstEncoder and ProstDecoder Default shouldn't require T: Default

[jrose-signal]

In tonic-prost 0.14.2, ProstEncoder and ProstDecoder both derive(Default). However, that makes their Default impl dependent on the message type also implementing Default, which is unnecessary.

Workaround: ProstEncoder::new(Default::default())

[LucioFranco]

Yeah this seems like an easy fix since relaxing the bound is not breaking.