Avoid ANSI codes in debug! messages (#15843)

## Summary

I spent time trying to figure out how to support this but came up empty.
It _seems_ like maybe the `DefaultFields` implementation in
`tracing-subscriber` uses debug formatting for fields...? So if you have
a string with ANSI codes, they end up printing as unformatted values? I
even reverted all our custom formatting in `logging.rs` and saw the same
thing.

Closes https://github.com/astral-sh/uv/issues/15840.

crates/uv-python/src/downloads.rs

@@ -1728,8 +1728,8 @@ mod tests {
             request.version,
             Some(VersionRequest::from_str("3.13.0rc1").unwrap())
         );
-        assert_eq!(request.os, None,);
-        assert_eq!(request.arch, None,);
+        assert_eq!(request.os, None);
+        assert_eq!(request.arch, None);
         assert_eq!(request.libc, None);
     }