Update record type computation

This commit refactors the way record types are computed within the
optimizer. Previously, the optimizer would often reuse the existing
`NodeMetrics` for records, which could lead to stale or polymorphic
types.

The changes introduce a new function, `compute_record_type`, which
explicitly recalculates the `StaticType` for a `Record` node based on
the concrete types of its child fields. This ensures that after
optimizations like inlining and folding, record types are as concrete as
possible, eliminating unresolved `TypeVars`.

Additionally, the `folder.rs` module is updated to recompute the
`RecordLayout` when creating constant record values, further improving
type accuracy. Two new tests are added to verify that inlined records,
including those with multiple fields, correctly result in concrete
types.

tests/optimizer.rs

@@ -277,3 +277,36 @@ fn test_block_and_lambda_propagate_concrete_type_after_inlining() {
         "Block type must be concrete. Line:\n{block_line}"
     );
 }
+
+// ── Record type recomputation after inlining ────────────────────────────────
+
+#[test]
+fn test_inlined_record_has_concrete_type() {
+    // A polymorphic function returning a record, called with a concrete arg.
+    // After inlining + folding, the record type must be concrete (no TypeVars).
+    let env = Environment::new();
+    let source = r#"(do
+        (def wrap (fn [x] {:val x}))
+        (wrap 42)
+    )"#;
+    let dump = env.dump_ast_compact(source).unwrap();
+    assert!(
+        !dump.contains('?'),
+        "Inlined record must not contain unresolved TypeVars. Dump:\n{dump}"
+    );
+}
+
+#[test]
+fn test_inlined_record_has_concrete_type_multi_field() {
+    // Heterogeneous case: Int + String fields should produce concrete record type.
+    let env = Environment::new();
+    let source = r#"(do
+        (def mkr (fn [a b] {:x a :y b}))
+        (mkr 1 "hello")
+    )"#;
+    let dump = env.dump_ast_compact(source).unwrap();
+    assert!(
+        !dump.contains('?'),
+        "Inlined multi-field record must not contain unresolved TypeVars. Dump:\n{dump}"
+    );
+}