Replace starlette.datastructures.Headers and other MultiDict-like structures with aio-libs/multidict

[jtraub]

As a part of migration from Starlette we should replace starlette.datastructures.Headers, starlette.datastructures.MutableHeaders and starlette.datastructures.ImmutableMultiDict with another multidict implementation.

Proposed library is multidict

Convenient usage list for mentioned classes can be found in #634

Related issue in starlite-multipart tracker - litestar-org/starlite-multipart#5

[Goldziher]

It occurs to me we can create our own version using https://docs.python.org/3/library/collections.html#collections.ChainMap

This has the advantage if being both fast and a builtin. It's not a multidict, but we can use it as a basis.

Thoughts?

[provinzkraut]

We could, but I'm not sure if we should. I don't think it's that fast, certainly not faster than the proposed multidict. And we'd have to add most of the implementation, not sure if there's really any benefit to using ChainMap here really (or maybe you have some genius idea on how to do that, that I just can't see? 🙃 If so, please do share!).

[Goldziher]

We could, but I'm not sure if we should. I don't think it's that fast, certainly not faster than the proposed multidict. And we'd have to add most of the implementation, not sure if there's really any benefit to using ChainMap here really (or maybe you have some genius idea on how to do that, that I just can't see? 🙃 If so, please do share!).

Nothing genius I'm afraid. Let's stick with multidicting This

[provinzkraut]

I had this on my plate already, unless @jtraub wants to take this on I'd take care of it in the following days?

[provinzkraut]

Implemented in #732