feat(nix/sparseTree): add optional name argument

This allows pinning the name of the sparse tree derivation, which
stops the continous rebuilding of tvix-store-proto dependents.

I've opted to let the function take an attribute set instead and
refactored the call sites appropriately.

Change-Id: I3e57785094b1adbfffa24caf9f1c3384844fa200
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8965
Reviewed-by: grfn <grfn@gws.fyi>
Tested-by: BuildkiteCI
Reviewed-by: sterni <sternenseemann@systemli.org>

users/grfn/xanthous/server/default.nix

@@ -10,10 +10,13 @@ depot.third_party.naersk.buildPackage {
 
   # Workaround for a potential Nix bug related to restricted eval.
   # See https://github.com/nix-community/naersk/issues/169
-  root = depot.nix.sparseTree ./. [
-    ./Cargo.toml
-    ./Cargo.lock
-  ];
+  root = depot.nix.sparseTree {
+    root = ./.;
+    paths = [
+      ./Cargo.toml
+      ./Cargo.lock
+    ];
+  };
 
   passthru = {
     docker = import ./docker.nix args;

users/tazjin/tgsa/default.nix

@@ -1,11 +1,14 @@
 { depot, pkgs, ... }:
 
 depot.third_party.naersk.buildPackage {
-  src = depot.nix.sparseTree ./. [
-    ./Cargo.lock
-    ./Cargo.toml
-    ./src
-  ];
+  src = depot.nix.sparseTree {
+    root = ./.;
+    paths = [
+      ./Cargo.lock
+      ./Cargo.toml
+      ./src
+    ];
+  };
 
   buildInputs = with pkgs; [
     pkg-config