Implements CborPacked, a more compressed variant of CBOR.

[ctm]

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[ctm]

This is a heads-up that we may want to change or replace CborPacked before the next version of yew is released.

Starting with serde_cbor 0.10, using to_vec_packed is no longer as compact for enums where the variant contains data. This was changed so that serde_cbor's format is now the serde preferred external tag format.

It is, however, possible to get the 0.9 level of compactness, and for my project, that's what I want. I suspect that others who would use CborPacked would want this as well, and that very few would want what we currently get when using to_vec_packed, because all enum variants that carry data will have the name of the variant transmitted.

Although serde_cbor 0.10 was released in July, I only noticed this issue a couple days ago due to me not having looked at any serialized data since upgrading to 0.10. I reported what appeared to me to be a regression and now that I better understand the situation, I'm going to submit a PR or two to help clarify the situation, but it looks like we'll probably not want to use to_vec_packed.

Once I know what's accepted over there, I'll propose a way to integrate it over here. I'm only mentioning it now, just in case there's a new release of yew imminent, in which case you may want to revert this before such a release so that the API doesn't churn as we nail things down.