fix(nix-compat/nar/reader): require BufRead

We rely on being able to make small reads cheaply, so this was already
an implicit practical requirement. Requiring it explicitly removes a
performance footgun, and makes further optimisations possible.

Change-Id: I7f65880a41b1d6b5e6bf2e52dfe47d4c49b34bcd
Reviewed-on: https://cl.tvl.fyi/c/depot/+/10088
Tested-by: BuildkiteCI
Reviewed-by: flokli <flokli@flokli.de>

tvix/store/src/nar/import.rs

@@ -1,5 +1,5 @@
 use std::{
-    io::{self, Read},
+    io::{self, BufRead},
     sync::Arc,
 };
 
@@ -21,7 +21,7 @@ use tvix_castore::{
 /// This function is not async (because the NAR reader is not)
 /// and calls [tokio::task::block_in_place] when interacting with backing
 /// services, so make sure to only call this with spawn_blocking.
-pub fn read_nar<R: Read + Send>(
+pub fn read_nar<R: BufRead + Send>(
     r: &mut R,
     blob_service: Arc<dyn BlobService>,
     directory_service: Arc<dyn DirectoryService>,