Test large numbers of keys in the database

Primarily to test garbage collection, but testing on a device with lots
of keys also showed some other slow operations so test those too.

Test: keystore2_test
Bug: 319563050
Change-Id: I308451992aa7cd6fd1a0fa43f0c113228ae7845d
diff --git a/keystore2/src/metrics_store.rs b/keystore2/src/metrics_store.rs
index 5a76d04..a55e52f 100644
--- a/keystore2/src/metrics_store.rs
+++ b/keystore2/src/metrics_store.rs
@@ -519,7 +519,7 @@
     }
 }
 
-fn pull_storage_stats() -> Result<Vec<KeystoreAtom>> {
+pub(crate) fn pull_storage_stats() -> Result<Vec<KeystoreAtom>> {
     let mut atom_vec: Vec<KeystoreAtom> = Vec::new();
     let mut append = |stat| {
         match stat {