Add MessagePack codec

[johnbchron]

This adds MessagePack codec support.

To quote MessagePack, "it's like JSON but fast and small". I was wanting to make a param payload that included a decently-sized byte array inline, and JSON is pretty inefficient at that, so I added MessagePack support.

The CI hasn't finished running on my machine but I decided to go ahead and submit it anyways because the change is so isolated.

[gbj]

Thanks, it's great to have added implementations like this. See notes above about into_string vs into_bytes.

[benwis]

I think there is a deeper question here, of how many codecs we want to have available in leptos itself. I don't think this is an issue for MessagePack or this commit, but it's worth thinking about moving forward

[benwis]

Overall this looks good, thanks for contributing!

[luckynumberke7in]

I think there is a deeper question here, of how many codecs we want to have available in leptos itself. I don't think this is an issue for MessagePack or this commit, but it's worth thinking about moving forward

I haven't worked with this package before, so someone please feel free to correct me, but from skimming the package...honestly...should something like this be a flat replacement in most cases (1:1)?

These little improvements towards an optimal Leptos sound wonderful, especially for a nosql or graphql DB when possible.

[benwis]

I think there is a deeper question here, of how many codecs we want to have available in leptos itself. I don't think this is an issue for MessagePack or this commit, but it's worth thinking about moving forward

I haven't worked with this package before, so someone please feel free to correct me, but from skimming the package...honestly...should something like this be a flat replacement in most cases (1:1)?

These little improvements towards an optimal Leptos sound wonderful, especially for a nosql or graphql DB when possible.

A flat replacement? This isn't really for db access, this is for the server fn encoding between server and client.