Test the rest of the worker protocol serializers

Part of the `BuildResult` test is commented out because we have caught a
roundtrip bug! A future PR will fix the bug and uncomment that test.

src/libstore/build-result.cc

@@ -0,0 +1,18 @@
+#include "build-result.hh"
+
+namespace nix {
+
+GENERATE_CMP_EXT(
+    ,
+    BuildResult,
+    me->status,
+    me->errorMsg,
+    me->timesBuilt,
+    me->isNonDeterministic,
+    me->builtOutputs,
+    me->startTime,
+    me->stopTime,
+    me->cpuUser,
+    me->cpuSystem);
+
+}