Fix hashing for integer plists (#5807)

lib/dicthf.gi

@@ -164,7 +164,7 @@ function(m, v)
     if not IsPlistRep(x) then
       x := AsPlist(x);
     fi;
-    return HashKeyWholeBag(x, 1);
+    return HashKeyBag(x, 1, 0, Length(x) * GAPInfo.BytesPerVariable);
   end;
 
   # alternative code w/o HashKeyBag

tst/testbugfix/2024-10-11-orbit-hash.tst

@@ -0,0 +1,20 @@
+# Fix a bug reported by Leonard Soicher caused by a bug in
+# the hash function for lists of small positive integers.
+gap> n:=280;;
+gap> G:=OnePrimitiveGroup(NrMovedPoints,n,Size,604800*2);
+J_2.2
+gap> blocks := [ [ 1, 2, 3, 28, 108, 119, 155, 198, 216, 226 ],
+>  [ 1, 2, 3, 118, 119, 140, 193, 213, 218, 226 ] ];;
+gap> Append(blocks[2],[1..1000]); for i in [1..1000] do Remove(blocks[2]); od;
+gap> Append(blocks[2],[1..1000]); for i in [1..1000] do Remove(blocks[2]); od;
+gap> ForAll(blocks,IsSet);
+true
+gap> orb1:=Orbit(G,blocks[1],OnSets);;
+gap> Length(orb1);
+12096
+gap> orb2:=Orbit(G,blocks[2],OnSets);;
+gap> Length(orb2);
+1008
+gap> orbs:=Orbits(G,blocks,OnSets);;
+gap> List(orbs,Length); # this code gave wrong results
+[ 12096, 1008 ]