Helpers to transform Twisted requests to Rust http Requests/Responses (#17081)

This adds functions to transform a Twisted request to the
`http::Request`, and then to send back an `http::Response` through it.

It also imports the SynapseError exception so that we can throw that
from Rust code directly

Example usage of this would be:

```rust
use crate::http::{http_request_from_twisted, http_response_to_twisted, HeaderMapPyExt};

fn handler(twisted_request: &PyAny) -> PyResult<()> {
    let request = http_request_from_twisted(twisted_request)?;

    let ua: headers::UserAgent = request.headers().typed_get_required()?;

    if whatever {
        return Err((crate::errors::SynapseError::new(
            StatusCode::UNAUTHORIZED,
            "Whatever".to_owned
            "M_UNAUTHORIZED",
            None,
            None,
        )));
    }

    let response = Response::new("hello".as_bytes());
    http_response_to_twisted(twisted_request, response)?;

    Ok(())
}
```

1 files changed, 2 insertions, 0 deletions

diff --git a/rust/src/lib.rs b/rust/src/lib.rs
index 7b3b579e55..36a3d64528 100644
--- a/rust/src/lib.rs
+++ b/rust/src/lib.rs
@@ -3,7 +3,9 @@ use pyo3::prelude::*;
 use pyo3_log::ResetHandle;
 
 pub mod acl;
+pub mod errors;
 pub mod events;
+pub mod http;
 pub mod push;
 
 lazy_static! {