chore: add vendor dependencies for kauma build

vendor/once_cell/examples/lazy_static.rs

@@ -0,0 +1,36 @@
+extern crate once_cell;
+
+use once_cell::sync::{Lazy, OnceCell};
+use std::collections::HashMap;
+
+static HASHMAP: Lazy<HashMap<u32, &'static str>> = Lazy::new(|| {
+    let mut m = HashMap::new();
+    m.insert(0, "foo");
+    m.insert(1, "bar");
+    m.insert(2, "baz");
+    m
+});
+
+// Same, but completely without macros
+fn hashmap() -> &'static HashMap<u32, &'static str> {
+    static INSTANCE: OnceCell<HashMap<u32, &'static str>> = OnceCell::new();
+    INSTANCE.get_or_init(|| {
+        let mut m = HashMap::new();
+        m.insert(0, "foo");
+        m.insert(1, "bar");
+        m.insert(2, "baz");
+        m
+    })
+}
+
+fn main() {
+    // First access to `HASHMAP` initializes it
+    println!("The entry for `0` is \"{}\".", HASHMAP.get(&0).unwrap());
+
+    // Any further access to `HASHMAP` just returns the computed value
+    println!("The entry for `1` is \"{}\".", HASHMAP.get(&1).unwrap());
+
+    // The same works for function-style:
+    assert_eq!(hashmap().get(&0), Some(&"foo"));
+    assert_eq!(hashmap().get(&1), Some(&"bar"));
+}