message: use the new `result_cache`
diff: @@ -17,6 +17,7 @@ use proptest::collection::{btree_map, btree_set, vec};
  use proptest::prelude::*;
  use proptest::sample::subsequence;
  use proptest::string::string_regex;
  +use proptest::test_runner::basic_result_cache;
  fn resolve(
  pkg: &PackageId,
  @@ -257,12 +258,18 @@ fn registry_strategy() -> impl Strategy<Value=Vec<Summary>> {
  }
  proptest! {
  + #![proptest_config(ProptestConfig {
  + result_cache: basic_result_cache,
  + cases: 256,
  + .. ProptestConfig::default()
  + })]
  #[test]
  fn doesnt_crash(input in registry_strategy()) {
  let reg = registry(input.clone());
  // there is only a small chance that eny one
  - // crate will be interesting. So we try them all.
  - for this in input.iter().rev() {
  + // crate will be interesting.
  + // So we some of the most complicated.
  + for this in input.iter().rev().take(100) {
  let res = resolve(
  &pkg_id("root"),
  vec![dep_req(&this.name(), &format!("={}", this.version()))],
  