expect parse seed in rng_from_time_or_env

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

core/storage/btree.rs

@@ -5776,7 +5776,7 @@ mod tests {
                 .duration_since(std::time::UNIX_EPOCH)
                 .unwrap()
                 .as_secs(),
-            |v| v.parse().unwrap(),
+            |v| v.parse().expect("Failed to parse SEED environment variable as u64"),
         );
         let rng = ChaCha8Rng::seed_from_u64(seed);
         (rng, seed)