chore: checkpoint before Python removal

vendor/minimal-lexical/tests/mask_tests.rs

@@ -0,0 +1,16 @@
+use minimal_lexical::mask;
+
+#[test]
+fn lower_n_mask_test() {
+    assert_eq!(mask::lower_n_mask(2), 0b11);
+}
+
+#[test]
+fn lower_n_halfway_test() {
+    assert_eq!(mask::lower_n_halfway(2), 0b10);
+}
+
+#[test]
+fn nth_bit_test() {
+    assert_eq!(mask::nth_bit(2), 0b100);
+}