Apply clang-format universally.

* It is tough to contribute to a project that doesn't use a formatter,
* It is extra hard to contribute to a project which has configured the formatter, but ignores it for some files
* Code formatting makes it harder to hide obscure / weird bugs by accident or on purpose,

Let's rip the bandaid off?

Note that PRs currently in flight should be able to be merged relatively easily by applying `clang-format` to their tip prior to merge.

src/libstore/derivation-options.cc

@@ -291,7 +291,7 @@ bool DerivationOptions::useUidRange(const BasicDerivation & drv) const
     return getRequiredSystemFeatures(drv).count("uid-range");
 }
 
-}
+} // namespace nix
 
 namespace nlohmann {
 
@@ -381,4 +381,4 @@ void adl_serializer<DerivationOptions::OutputChecks>::to_json(json & json, Deriv
     json["disallowedRequisites"] = c.disallowedRequisites;
 }
 
-}
+} // namespace nlohmann