Vendor dependencies

Let's see how I like this workflow.

vendor/anyhow/tests/ui/must-use.rs

@@ -0,0 +1,11 @@
+#![deny(unused_must_use)]
+
+use anyhow::anyhow;
+
+fn main() -> anyhow::Result<()> {
+    if true {
+        // meant to write bail!
+        anyhow!("it failed");
+    }
+    Ok(())
+}