Secret memory with memfd_secret (#321)

Implements:
- An additional allocator to use memfd_secret(2) and guard pages using mmap(2), implemented in quininer/memsec#16
- An allocator that abstracts away underlying allocators, and uses specified allocator set by rosenpass_secret_memory::policy functions (or a function that sets rosenpass_secret_memory::alloc::ALLOC_INIT
- Updates to tests- integration, fuzz, bench: some tests use procspawn to spawn multiple processes with different allocator policies

rp/src/main.rs

@@ -3,6 +3,7 @@ use std::process::exit;
 use cli::{Cli, Command};
 use exchange::exchange;
 use key::{genkey, pubkey};
+use rosenpass_secret_memory::policy;
 
 mod cli;
 mod exchange;
@@ -10,6 +11,8 @@ mod key;
 
 #[tokio::main]
 async fn main() {
+    policy::secret_policy_try_use_memfd_secrets();
+
     let cli = match Cli::parse(std::env::args().peekable()) {
         Ok(cli) => cli,
         Err(err) => {