Add an experimental, disabled 32 bit internal version

I think it's only missing detection for full-precision versions more
than 2e9 apart

Internal.h

@@ -578,8 +578,8 @@ template <class ConflictSetImpl> struct TestDriver {
   explicit TestDriver(const uint8_t *data, size_t size)
       : arbitrary({data, size}) {}
 
-  int64_t writeVersion = 100;
-  int64_t oldestVersion = 0;
+  int64_t oldestVersion = arbitrary.bounded(2) ? 0 : 0xfffffff0;
+  int64_t writeVersion = oldestVersion + 100;
   ConflictSetImpl cs{oldestVersion};
   ReferenceImpl refImpl{oldestVersion};