Vendor dependencies

Let's see how I like this workflow.

vendor/thiserror/tests/ui/transparent-enum-many.rs

@@ -0,0 +1,9 @@
+use thiserror::Error;
+
+#[derive(Error, Debug)]
+pub enum Error {
+    #[error(transparent)]
+    Other(anyhow::Error, String),
+}
+
+fn main() {}