chore: Reorganize memfd secret policy

- Policy is now set in main.rs, not cli.rs.
- Feature is called experiment_memfd_secret, not enable_memfd_alloc

This also fixes the last remaining warnings.

rp/Cargo.toml

@@ -39,5 +39,5 @@ tempfile = {workspace = true}
 stacker = {workspace = true}
 
 [features]
-enable_memfd_alloc = []
+experiment_memfd_secret = []
 experiment_libcrux = ["rosenpass-ciphers/experiment_libcrux"]

rp/src/main.rs

@@ -11,9 +11,9 @@ mod key;
 
 #[tokio::main]
 async fn main() {
-    #[cfg(feature = "enable_memfd_alloc")]
+    #[cfg(feature = "experiment_memfd_secret")]
     policy::secret_policy_try_use_memfd_secrets();
-    #[cfg(not(feature = "enable_memfd_alloc"))]
+    #[cfg(not(feature = "experiment_memfd_secret"))]
     policy::secret_policy_use_only_malloc_secrets();
 
     let cli = match Cli::parse(std::env::args().peekable()) {