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

include/xrpl/protocol/Serializer.h

@@ -27,9 +27,9 @@
 #include <xrpl/basics/contract.h>
 #include <xrpl/basics/safe_cast.h>
 #include <xrpl/basics/strHex.h>
+#include <xrpl/beast/utility/instrumentation.h>
 #include <xrpl/protocol/HashPrefix.h>
 #include <xrpl/protocol/SField.h>
-#include <cassert>
 #include <cstdint>
 #include <cstring>
 #include <iomanip>
@@ -55,7 +55,9 @@ public:
 
         if (size)
         {
-            assert(data != nullptr);
+            ASSERT(
+                data != nullptr,
+                "ripple::Serializer::Serializer(void const*) : non-null input");
             std::memcpy(mData.data(), data, size);
         }
     }
@@ -331,7 +333,7 @@ Serializer::addVL(Iter begin, Iter end, int len)
         len -= begin->size();
 #endif
     }
-    assert(len == 0);
+    ASSERT(len == 0, "ripple::Serializer::addVL : length matches distance");
     return ret;
 }