ZJIT: Add regression tests for important type sizes (ruby#17560)

We want to make sure these don't get any bigger and also ratchet down if we shrink them.

Author: tekknolagi

zjit/src/hir/tests.rs

@@ -1,6 +1,21 @@
 #[cfg(test)]
 use super::*;
 
+#[cfg(test)]
+mod size_tests {
+    use super::*;
+
+    #[test]
+    fn test_size_of_insn() {
+        assert_eq!(std::mem::size_of::<Insn>(), 120);
+    }
+
+    #[test]
+    fn test_size_of_type() {
+        assert_eq!(std::mem::size_of::<Type>(), 24);
+    }
+}
+
 #[cfg(test)]
 mod snapshot_tests {
     use super::*;