feat: userspace program loading and task spawning

userspace/echo/Cargo.toml

@@ -0,0 +1,12 @@
+[package]
+name = "echo"
+version = "0.1.0"
+edition = "2024"
+
+[dependencies]
+dusk-sys = { path = "../dusk-sys" }
+
+[[bin]]
+name = "echo"
+test = false
+bench = false

userspace/echo/src/main.rs

@@ -0,0 +1,23 @@
+#![no_std]
+#![no_main]
+
+use dusk_sys::{println, sys_exit, sys_recv, sys_send};
+
+#[unsafe(no_mangle)]
+pub extern "C" fn _start() -> ! {
+    let out = [0u8; 128];
+    loop {
+        let (actual_len, sender) = sys_recv(out.as_ptr() as usize, out.len()).unwrap();
+        println!(
+            "[echo] Received: {}",
+            core::str::from_utf8(&out[..actual_len]).unwrap()
+        );
+        sys_send(sender, out.as_ptr() as usize, actual_len).unwrap();
+    }
+}
+
+#[panic_handler]
+fn panic(info: &core::panic::PanicInfo) -> ! {
+    println!("{info}");
+    sys_exit(1);
+}