feat: add preliminary miri support

- Adds a devShell with Miri
- Marks some of the tests which Miri cannot execute as ignored for Miri

Signed-off-by: wucke13 <wucke13+github@gmail.com>

rp/tests/smoketest.rs

@@ -2,6 +2,7 @@ use std::process::Command;
 
 #[cfg(any(target_os = "linux", target_os = "freebsd"))]
 #[test]
+#[cfg_attr(miri, ignore)] // unsupported operation: extern static `pidfd_spawnp` is not supported by Miri
 fn smoketest() -> anyhow::Result<()> {
     let tmpdir = tempfile::tempdir()?;