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/basics/partitioned_unordered_map.h

@@ -20,7 +20,7 @@
 #ifndef RIPPLE_BASICS_PARTITIONED_UNORDERED_MAP_H
 #define RIPPLE_BASICS_PARTITIONED_UNORDERED_MAP_H
 
-#include <cassert>
+#include <xrpl/beast/utility/instrumentation.h>
 #include <functional>
 #include <optional>
 #include <thread>
@@ -246,7 +246,10 @@ public:
             ? *partitions
             : std::thread::hardware_concurrency();
         map_.resize(partitions_);
-        assert(partitions_);
+        ASSERT(
+            partitions_ != 0,
+            "ripple::partitioned_unordered_map::partitioned_unordered_map : "
+            "nonzero partitions");
     }
 
     std::size_t