Co-authored-by: Kunal Mehta <[email protected]>

Co-authored-by: Kunal Mehta <[email protected]>

We care about the preservation of the entire configured origin tuple
(scheme, host, port), not just the hostname.[1]  However, there is a
tension in considering whether this check is valuable:

1. On the one hand, as @legoktm has pointed out, if Url::parse() is
   compromised, why should we trust the result of Url::Url.origin()?

2. On the other hand, as Daniel Stenberg has documented, "mixing parsers
   is considered a security risk".[2]

[1]: https://url.spec.whatwg.org/#origin

[2]: https://daniel.haxx.se/blog/2022/01/10/dont-mix-url-parsers/

`process::exit()` immediately terminates with the given exit code,
meaning that no destructors are run. For our purposes it shouldn't
matter much, but let's exit the graceful way.

Rewrite the existing tests to be integration tests against a compiled
Rust binary. We use the httpbin library to start up a Python webserver
and instruct the proxy to connect to it. This allows to test connection
properties that aren't recordable in the VCR format, like timeouts or
streamed responses.

The tests are reorganized to be split into proxy handling and error
handling.

And remove the Python CI. We still need to set up cargo-audit and
cargo-vet jobs.