Add Antithesis intrumentation (#5042)

* Copy Antithesis SDK version 0.4.0 to directory external/
* Add build option `voidstar` to enable instrumentation with Antithesis SDK
* Define instrumentation macros ASSERT and UNREACHABLE in terms of regular C assert
* Replace asserts with named ASSERT or UNREACHABLE
* Add UNREACHABLE to LogicError
* Document instrumentation macros in CONTRIBUTING.md

src/test/jtx/impl/amount.cpp

@@ -20,7 +20,6 @@
 #include <test/jtx/Account.h>
 #include <test/jtx/amount.h>
 #include <xrpl/basics/safe_cast.h>
-#include <cassert>
 #include <cmath>
 #include <iomanip>
 

src/test/overlay/short_read_test.cpp

@@ -26,7 +26,6 @@
 #include <boost/asio/ssl.hpp>
 #include <boost/utility/in_place_factory.hpp>
 
-#include <cassert>
 #include <condition_variable>
 #include <functional>
 #include <memory>