refactor(tvix/store/nar): pass in &proto::node::Node

Passing in a &proto::node::Node into all this allows us consumers to
keep ownership of the proto::node::Node.

Change-Id: I44882a86c46826b06a8a8a0b24c18adfc7052662
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8316
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>
Autosubmit: flokli <flokli@flokli.de>

tvix/store/src/nar/mod.rs

@@ -31,6 +31,6 @@ pub enum RenderError {
 pub trait NARCalculationService {
     fn calculate_nar(
         &self,
-        root_node: proto::node::Node,
+        root_node: &proto::node::Node,
     ) -> Result<proto::CalculateNarResponse, RenderError>;
 }