feat: Recover from fallback writer state (#3000)

Add a timer and new `FallbackRecovery` state to try to recover from
`Fallback` writer state every hour.
Fixes #2997

src/cluster/impl/FallbackRecoveryTimer.cpp

@@ -0,0 +1,53 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of clio: https://github.com/XRPLF/clio
+    Copyright (c) 2025, the clio developers.
+
+    Permission to use, copy, modify, and distribute this software for any
+    purpose with or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL,  DIRECT,  INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include "cluster/impl/FallbackRecoveryTimer.hpp"
+
+#include "util/Mutex.hpp"
+
+#include <boost/asio/thread_pool.hpp>
+
+#include <chrono>
+#include <memory>
+
+namespace cluster::impl {
+
+FallbackRecoveryTimer::FallbackRecoveryTimer(
+    boost::asio::thread_pool& ctx,
+    std::chrono::steady_clock::duration recoveryTime
+)
+    : impl_(std::make_shared<util::Mutex<Impl>>(Impl{ctx.get_executor(), recoveryTime}))
+{
+}
+
+bool
+FallbackRecoveryTimer::isRunning() const
+{
+    return impl_->lock()->isRunning;
+}
+
+void
+FallbackRecoveryTimer::cancel()
+{
+    auto locked = impl_->lock();
+    locked->isRunning = false;
+    locked->timer.cancel();
+}
+
+}  // namespace cluster::impl