feat(tvix): set up cargo rust project

First steps for baba

Change-Id: Id6a68c5630cb85f280f4dcc7b2acf10c02454fd6
Reviewed-on: https://cl.tvl.fyi/c/depot/+/4732
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

tvix/.vscode/extensions.json

@@ -0,0 +1,8 @@
+{
+    "recommendations": [
+        "matklad.rust-analyzer"
+    ],
+    "unwantedRecommendations": [
+        "rust-lang.rust"
+    ]
+}