Include lb_tasklib::spawn in globals

crates/lb/src/task.lua

@@ -0,0 +1,6 @@
+local task = require("lb:task")
+
+-- include `lb_tasklib::spawn` in the global scope
+function spawn(f, ...)
+  return task:spawn(f, ...)
+end

crates/lb/src/task.rs

@@ -7,6 +7,7 @@ use tokio::task::JoinHandle;
 pub struct lb_tasklib;
 
 #[metatype]
+#[include("task.lua")]
 impl lb_tasklib {
     #[new]
     extern "Lua-C" fn new() -> Self {