Preserve HTTP version in twirp client response

[itsibitzi]

Motivation

While testing the http/2 rollout I noticed that there was a up-tick in HTTP/2 requests coming in but the client send metrics were all saying HTTP/1.1.

It turns out this is because we were manually reconstructing a http::Response in the twirp client, without propagating the version.

Implementation

Copied across the version like we do with the status etc.

[Copilot]

Pull Request Overview

This PR fixes a bug where the HTTP version was not being preserved when reconstructing HTTP responses in the Twirp client, causing metrics to incorrectly report all requests as HTTP/1.1 instead of their actual version (e.g., HTTP/2).

• Extract the HTTP version from the original response before consuming it
• Set the version on the reconstructed response object alongside existing headers and extensions

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