More std::filesystem::path for nix {cat,ls}

Also fixes a double quoting issue I accidentally introduced ccdd1f1c65
in seekableGetNarBytes.

src/libutil/nar-accessor.cc

@@ -268,7 +268,7 @@ GetNarBytes seekableGetNarBytes(const std::filesystem::path & path)
 {
     AutoCloseFD fd = openFileReadonly(path);
     if (!fd)
-        throw NativeSysError("opening NAR cache file '%s'", path);
+        throw NativeSysError("opening NAR cache file %s", path);
 
     return [inner = seekableGetNarBytes(fd.get()), fd = make_ref<AutoCloseFD>(std::move(fd))](
                uint64_t offset, uint64_t length) { return inner(offset, length); };

src/nix/cat.cc

@@ -52,7 +52,7 @@ struct CmdCatStore : StoreCommand, MixCat
 
 struct CmdCatNar : StoreCommand, MixCat
 {
-    Path narPath;
+    std::filesystem::path narPath;
 
     std::string path;
 
@@ -76,9 +76,9 @@ struct CmdCatNar : StoreCommand, MixCat
 
     void run(ref<Store> store) override
     {
-        AutoCloseFD fd = toDescriptor(open(narPath.c_str(), O_RDONLY));
+        AutoCloseFD fd = openFileReadonly(narPath);
         if (!fd)
-            throw SysError("opening NAR file '%s'", narPath);
+            throw NativeSysError("opening NAR file %s", narPath);
         auto source = FdSource{fd.get()};
 
         struct CatRegularFileSink : NullFileSystemObjectSink

src/nix/ls.cc

@@ -126,7 +126,7 @@ struct CmdLsStore : StoreCommand, MixLs
 
 struct CmdLsNar : Command, MixLs
 {
-    Path narPath;
+    std::filesystem::path narPath;
 
     std::string path;
 
@@ -150,9 +150,9 @@ struct CmdLsNar : Command, MixLs
 
     void run() override
     {
-        AutoCloseFD fd = toDescriptor(open(narPath.c_str(), O_RDONLY));
+        AutoCloseFD fd = openFileReadonly(narPath);
         if (!fd)
-            throw SysError("opening NAR file '%s'", narPath);
+            throw NativeSysError("opening NAR file %s", narPath);
         auto source = FdSource{fd.get()};
         list(makeLazyNarAccessor(source, seekableGetNarBytes(fd.get())), CanonPath{path});
     }