test(3p/nix): Add property tests for attribute set

Add a set of property tests for the attribute set (Bindings) class
checking that the Merge operation satisfies the monoid laws. This
will hopefully become useful to make sure we're not breaking the
language semantics as we work towards optimizing or replacing the
implementation, but also serves as a test bed for adding
rapidcheck-based property tests to the codebase.

Change-Id: I1b4b7b6503d08d80c1c5a8f9408fd4b787d00e8e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/1283
Reviewed-by: isomer <isomer@tvl.fyi>
Tested-by: BuildkiteCI

third_party/nix/default.nix

@@ -55,7 +55,6 @@ in pkgs.llvmPackages.libcxxStdenv.mkDerivation {
     flex
     glog
     grpc
-    gtest
     libseccomp
     libsodium
     openssl
@@ -67,6 +66,11 @@ in pkgs.llvmPackages.libcxxStdenv.mkDerivation {
   doCheck = false;
   doInstallCheck = true;
 
+  installCheckInputs = with pkgs; [
+    gtest
+    rapidcheck
+  ];
+
   propagatedBuildInputs = with pkgs; [
     boost
     largeBoehm