chore(tvix/derivation): align json serialization with nix output

Use the #[serde(rename = "…")] field attributes to match the field names
that Nix uses in its JSON output (nix show-derivation).

This allows us to just re-use the exact same fixtures from go-nix,
without manual post-massaging.

Change-Id: Ifd5c08e43cd4f50d5e02903eccd8cb37230b70a6
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7757
Reviewed-by: jrhahn <mail.jhahn@gmail.com>
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

tvix/derivation/src/output.rs

@@ -12,7 +12,7 @@ pub struct Output {
 pub struct Hash {
     #[serde(rename = "hash")]
     pub digest: String,
-    #[serde(rename = "hash_algorithm")]
+    #[serde(rename = "hashAlgo")]
     pub algo: String,
 }