Update duckdb index files

.gitattributes

@@ -4,3 +4,4 @@ bicubic_x4/train/index.duckdb filter=lfs diff=lfs merge=lfs -text
 bicubic_x4/validation/index.duckdb filter=lfs diff=lfs merge=lfs -text
 bicubic_x8/train/index.duckdb filter=lfs diff=lfs merge=lfs -text
 bicubic_x8/validation/index.duckdb filter=lfs diff=lfs merge=lfs -text
+realistic_difficult_x4/train/index.duckdb filter=lfs diff=lfs merge=lfs -text

realistic_difficult_x4/train/index.duckdb

@@ -0,0 +1,3 @@
+version https://git-lfs.github.com/spec/v1
+oid sha256:ec5860015c76f7999f61f1793f8e3b6bc76280c62354a2c2014a6a7baebfad03
+size 1060864