SQL pools time out; task locks are a renewed five-minute lease

A 3-node rehearsal (PostgreSQL + NATS + Garage) found two ways a crash
leaves work stuck:

Pool hangs. The PostgreSQL pool (deadpool) was built with no timeouts,
so a request waited for a free connection, and for one to be opened or
recycled, for as long as it took: forever when the server stopped
answering. MySQL's pool (mysql_async) has no wait timeout at all.

- PostgreSQL: wait 30 s (or the store's timeout if longer), create the
  store's timeout or 15 s (it bounds the whole handshake, where
  tokio-postgres's connect_timeout covers only the TCP connect), recycle
  10 s. The pool config is now always set, not only with
  poolMaxConnections.
- MySQL: every connection is taken through MysqlStore::conn(), which
  gives up after 30 s.
- Both: TCP keepalive after 60 s idle, so a server that vanished
  without closing the connection is noticed in minutes rather than the
  two-hour system default.

The DataStore schema has no pool timeout settings, so these are fixed
defaults; the store's own timeout bounds connecting on PostgreSQL.

Task locks. A task lock lasted an hour, so after a hard crash the dead
node's tasks waited up to an hour and five minutes. The lock is now a
five-minute lease: while this node runs a task, the task manager renews
its lock every third of the lifetime (InMemoryStore::renew_lock, a
compare-and-set on the store backends and SET XX EX on Redis, which
leaves a lock that already expired alone). A killed node's tasks run
elsewhere within about five minutes plus the claim recheck. A task this
node holds isn't handed to a worker again by the scan.

store::pool_timeout (new): a local listener that accepts connections
and never answers plays a hung server; a PostgreSQL store with a 2 s
timeout returns an error in about 4 s, and a MySQL store in 30 s.
Without the timeouts both wait for good. store::task_locks gains a
task held for 1.5 lock lifetimes: its lease is still held, and released
when the task ends.

tests/src/store/task_locks.rs

@@ -79,7 +79,33 @@ pub async fn task_lock_tests() {
         "ran before the other node's locks expired: {elapsed:?}"
     );
 
-    // 3. A graceful stop releases the locks this node holds: another node
+    // 3. A task that runs longer than a lock lifetime keeps its claim: the
+    // task manager renews the lease while this node holds it, and the claim
+    // ends when the task does. (Before, a lock simply lasted an hour.)
+    let [id] = new_task_ids(1)[..] else {
+        unreachable!()
+    };
+    assert!(server.try_lock_task(id).await, "claim {id}");
+    tokio::time::sleep(Duration::from_secs(LOCK_EXPIRY + LOCK_EXPIRY / 2)).await;
+    assert!(
+        !foreign_lock(&server, id, LOCK_EXPIRY).await,
+        "lease lapsed while the task ran"
+    );
+    server.remove_index_lock(id).await;
+    assert!(
+        foreign_lock(&server, id, LOCK_EXPIRY).await,
+        "released when the task ended"
+    );
+    let _ = server
+        .in_memory_store()
+        .remove_lock(KV_LOCK_TASK, &id.to_be_bytes())
+        .await;
+    assert!(
+        common::ipc::TaskLocks::DEFAULT_EXPIRY <= 5 * 60,
+        "a dead node's tasks wait no more than a few minutes"
+    );
+
+    // 4. A graceful stop releases the locks this node holds: another node
     // can claim those tasks at once, and this one claims nothing more
     let ids = new_task_ids(3);
     for id in &ids {