fix(tvix/castore): instrument blob uploads with current span

Change-Id: I67e18486c48f06787fad8be506e95eecc23e994d
Reviewed-on: https://cl.tvl.fyi/c/depot/+/12825
Reviewed-by: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
Reviewed-by: Jonas Chevalier <zimbatm@zimbatm.com>

tvix/castore/src/import/blobs.rs

@@ -9,6 +9,7 @@ use tokio::{
     task::{JoinError, JoinSet},
 };
 use tokio_util::io::InspectReader;
+use tracing::{info_span, Instrument};
 
 use crate::{blobservice::BlobService, B3Digest, Path, PathBuf};
 
@@ -140,6 +141,7 @@ where
                     drop(permit);
                     Ok(())
                 }
+                .instrument(info_span!("upload_task"))
             });
 
             return Ok(digest);