Support underscore int read instruction (#7488)

support underscore int read instruction

Author: lhoestq

src/datasets/arrow_reader.py

@@ -48,10 +48,10 @@
 ^
  (?P<split>{_split_re[1:-1]})
  (\[
-    ((?P<from>-?\d+)
+    ((?P<from>-?[\d_]+)
      (?P<from_pct>%)?)?
     :
-    ((?P<to>-?\d+)
+    ((?P<to>-?[\d_]+)
      (?P<to_pct>%)?)?
  \])?(\((?P<rounding>[^\)]*)\))?
 $