feat(follow_redirect): Preserve extensions during redirection

[0x676e67]

Motivation

Extensions are passed during request redirection. Extensions that currently rely on http 1.x are now cloneable.

https://github.com/hyperium/http/blob/613d3d465f222666327d61f5971133cad155f190/src/extensions.rs#L35

Solution

Solve some scenarios where redirection requires passing Extensions

[0x676e67]

Is this approach justifiable?

[0x676e67]

Four hours ago, tracing-core updated its version and upgraded msrv. CI seems to have failed because of this.

[tesaguri]

Although I was not involved in #348, I guess it was a mere oversight that the design decision to drop extensions hadn't been revisited in the migration to http v1.

That said, I think it's a breaking change so the commit message should clearly make that clear, as required in the CONTRIBUTING.md. But, well, the contributing guidelines also prohibit one from rebasing the branch after opening a PR. I wonder how are non-conforming commit messages supposed to be handled then?

[jplatte]

Well, FWIW I didn't know this repo had a CONTRIBUTING.md 😅
@seanmonstar do you care about the stuff in there? In particular force-pushes to PRs?

[seanmonstar]

Eh, I don't know where all that came from, was it imported from Tokio?

I don't personally care if people force push PRs. I know some people like to see the incremental changes after review passes, but I always have to review the entire change before I click merge, so I don't care.