starlark: optimize repeat (#28)
starlark: optimize repeat (#28)

Using these benchmarks:

def bench_repeat_short_tuple_10():
  10 * ("a", "b", "c")

def bench_repeat_short_tuple_10k():
  10000 * ("a", "b", "c")

def bench_repeat_short_tuple_10m():
  10000000 * ("a", "b", "c")

results:

name                                             old time/op  new time/op  delta
File/bench_repeat.star/repeat_short_tuple_10-8    567ns ± 0%   523ns ± 0%    -7.68%  (p=0.000 n=10+8)
File/bench_repeat.star/repeat_short_tuple_10k-8   255µs ± 0%   158µs ± 0%   -38.25%  (p=0.000 n=9+10)
File/bench_repeat.star/repeat_short_tuple_10m-8   594ms ± 1%   510ms ± 5%   -14.19%  (p=0.000 n=9+9)
google/starlark-go,google/starlark-go