fuzz: make it possible to mock (fuzz) CThreadInterrupt

* Make the methods of `CThreadInterrupt` virtual and store a pointer to
  it in `CConnman`, thus making it possible to override with a mocked
  instance.
* Initialize `CConnman::m_interrupt_net` from the constructor, making it
  possible for callers to supply mocked version.
* Introduce `FuzzedThreadInterrupt` and `ConsumeThreadInterrupt()` and
  use them in `src/test/fuzz/connman.cpp` and `src/test/fuzz/i2p.cpp`.

This improves the CPU utilization of the `connman` fuzz test.

As a nice side effect, the `std::shared_ptr` used for
`CConnman::m_interrupt_net` resolves the possible lifetime issues with
it (see the removed comment for that variable).

src/test/fuzz/util/threadinterrupt.cpp

@@ -0,0 +1,22 @@
+// Copyright (c) 2024-present The Bitcoin Core developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include <test/fuzz/util.h>
+#include <test/fuzz/util/threadinterrupt.h>
+
+FuzzedThreadInterrupt::FuzzedThreadInterrupt(FuzzedDataProvider& fuzzed_data_provider)
+    : m_fuzzed_data_provider{fuzzed_data_provider}
+{
+}
+
+bool FuzzedThreadInterrupt::interrupted() const
+{
+    return m_fuzzed_data_provider.ConsumeBool();
+}
+
+bool FuzzedThreadInterrupt::sleep_for(Clock::duration)
+{
+    SetMockTime(ConsumeTime(m_fuzzed_data_provider)); // Time could go backwards.
+    return m_fuzzed_data_provider.ConsumeBool();
+}