feat(tvix/derivation): make struct members public

Allow others to peek into values. We should probably still restrict
this further at a later point.

Change-Id: I2831432038aa87c3c7dcc85af4fa76a4fe0eadff
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7745
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI

tvix/derivation/src/derivation.rs

@@ -9,13 +9,13 @@ use tvix_store::nixpath::STORE_DIR;
 
 #[derive(Serialize, Deserialize)]
 pub struct Derivation {
-    outputs: BTreeMap<String, Output>,
-    input_sources: Vec<String>,
-    input_derivations: BTreeMap<String, Vec<String>>,
-    platform: String,
-    builder: String,
-    arguments: Vec<String>,
-    environment: BTreeMap<String, String>,
+    pub outputs: BTreeMap<String, Output>,
+    pub input_sources: Vec<String>,
+    pub input_derivations: BTreeMap<String, Vec<String>>,
+    pub platform: String,
+    pub builder: String,
+    pub arguments: Vec<String>,
+    pub environment: BTreeMap<String, String>,
 }
 
 impl Derivation {