lib.lists: add replicate

`replicate` returns n copies of an element as a list.

Co-Authored-By: Silvan Mosberger <contact@infinisil.com>

lib/tests/misc.nix

@@ -459,6 +459,11 @@ runTests {
     expected = [2 30 40 42];
   };
 
+  testReplicate = {
+    expr = replicate 3 "a";
+    expected = ["a" "a" "a"];
+  };
+
   testToIntShouldConvertStringToInt = {
     expr = toInt "27";
     expected = 27;