index: on reindexing, print error details to stderr

It's not ideal to print the error there, but using stderr should be slightly
better. It could be a tracing message, but tracing won't be displayed by
default.

lib/src/default_index/store.rs

@@ -331,7 +331,7 @@ impl IndexStore for DefaultIndexStore {
                 // If the index was corrupt (maybe it was written in a different format),
                 // we just reindex.
                 // TODO: Move this message to a callback or something.
-                println!("The index was corrupt (maybe the format has changed). Reindexing...");
+                eprintln!("{err}: {source}. Reindexing...", source = err.error);
                 self.reinit().map_err(|err| IndexReadError(err.into()))?;
                 self.build_index_segments_at_operation(op, store)
             }