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/libutil/signature/signer.cc

@@ -8,7 +8,8 @@ namespace nix {
 LocalSigner::LocalSigner(SecretKey && privateKey)
     : privateKey(privateKey)
     , publicKey(privateKey.toPublicKey())
-{ }
+{
+}
 
 std::string LocalSigner::signDetached(std::string_view s) const
 {
@@ -20,4 +21,4 @@ const PublicKey & LocalSigner::getPublicKey()
     return publicKey;
 }
 
-}
+} // namespace nix