Vendor dependencies

Let's see how I like this workflow.

vendor/lock_api/build.rs

@@ -0,0 +1,7 @@
+fn main() {
+    let cfg = autocfg::new();
+
+    if cfg.probe_rustc_version(1, 61) {
+        println!("cargo:rustc-cfg=has_const_fn_trait_bound");
+    }
+}