chore: checkpoint before Python removal

vendor/rustls/build.rs

@@ -0,0 +1,13 @@
+//! This build script allows us to enable the `read_buf` language feature only
+//! for Rust Nightly.
+//!
+//! See the comment in lib.rs to understand why we need this.
+
+#[cfg_attr(feature = "read_buf", rustversion::not(nightly))]
+fn main() {}
+
+#[cfg(feature = "read_buf")]
+#[rustversion::nightly]
+fn main() {
+    println!("cargo:rustc-cfg=read_buf");
+}