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.

crates/store/src/backend/mysql/search.rs

@@ -26,7 +26,7 @@ use std::fmt::Write;
 
 impl MysqlStore {
     pub async fn index(&self, documents: Vec<IndexDocument>) -> trc::Result<()> {
-        let mut conn = self.conn_pool.get_conn().await.map_err(into_error)?;
+        let mut conn = self.conn().await?;
         let mut tx_opts = TxOpts::default();
         tx_opts
             .with_consistent_snapshot(false)
@@ -96,7 +96,7 @@ impl MysqlStore {
             build_sort(&mut query, sort);
         }
 
-        let mut conn = self.conn_pool.get_conn().await.map_err(into_error)?;
+        let mut conn = self.conn().await?;
         let s = conn.prep(query).await.map_err(into_error)?;
 
         conn.exec::<i64, _, _>(s, params)
@@ -110,7 +110,7 @@ impl MysqlStore {
         let mut query = format!("DELETE FROM {table} ");
         let params = build_filter(&mut query, &filter.filters);
 
-        let mut conn = self.conn_pool.get_conn().await.map_err(into_error)?;
+        let mut conn = self.conn().await?;
         let s = conn.prep(&query).await.map_err(into_error)?;
 
         match conn.exec_drop(s, params.clone()).await {