chore: Nat.repr microbenchmark (#3888)

tests/bench/nat_repr.lean

@@ -0,0 +1,8 @@
+def main : List String → IO Unit
+| [n] => do
+  let mut s := 0
+  for i in [0:n.toNat!] do
+    for j in [:i] do
+      s := s + j.repr.length
+  IO.println s
+| _ => throw $ IO.userError "give upper bound"

tests/bench/nat_repr.lean.args

@@ -0,0 +1 @@
+5000

tests/bench/nat_repr.lean.expected.out

@@ -0,0 +1 @@
+44945605

tests/bench/speedcenter.exec.velcom.yaml

@@ -302,6 +302,14 @@
   run_config:
     <<: *time
     cmd: lean reduceMatch.lean
+- attributes:
+    description: nat_repr
+    tags: [fast, suite]
+  run_config:
+    <<: *time
+    cmd: ./nat_repr.lean.out 5000
+  build_config:
+    cmd: ./compile.sh nat_repr.lean
 - attributes:
     description: unionfind
     tags: [fast, suite]