Issue with saving long values in a document

When we try to save a long value into a map entry, it seems like it is saved as a float value. Following code prints "F64" as the type

```
import org.automerge.*;

import java.util.Optional;

public class IntFloatIssue {

public static void main(String args[]) {
Document doc = new Document();
ObjectId annoMapObj;
try (Transaction tx = doc.startTransaction()) {
annoMapObj = tx.set(ObjectId.ROOT, "annotations", ObjectType.MAP);
long value = 10000000000L;
tx.set(annoMapObj, "longval", value);
tx.commit();
}

Optional amValue = doc.get(annoMapObj, "longval");
System.out.println(amValue.get().getClass().getSimpleName());
}
}
```

Run the supplied Java reproducer first, then trace Document.get and Transaction.set around numeric value handling. Done means storing 10000000000L in the map returns a long or integer value rather than F64, with a regression test covering the case.

Written by the indexing model from the issue text.