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.

Co-authored-by: Graham Christensen <graham@grahamc.com>

src/libcmd/command-installable-value.cc

@@ -8,4 +8,4 @@ void InstallableValueCommand::run(ref<Store> store, ref<Installable> installable
     run(store, installableValue);
 }
 
-}
+} // namespace nix