Add inheritance module: SINGLE_TABLE vs JOINED vs TABLE_PER_CLASS on Hibernate 7.4.13.Final

Same payment hierarchy mapped three ways plus @MappedSuperclass, run with plain Hibernate on H2.
Tests assert and write the generated DDL, the INSERT/SELECT SQL, row/insert/FK/nullability counts and
the three failures (NOT NULL on a SINGLE_TABLE subclass column, IDENTITY with TABLE_PER_CLASS, querying a
@MappedSuperclass); Bench writes indicative polymorphic-query timings. No docs folder: depth lives in the post.

inheritance/output/01-ddl-mapped-superclass.txt

@@ -0,0 +1,22 @@
+-- DDL generated by Hibernate 7.4.13.Final for H2, @MappedSuperclass AuditedBase + Invoice + Receipt
+
+
+    create sequence mp_invoice_SEQ start with 1 increment by 50;
+
+    create sequence mp_receipt_SEQ start with 1 increment by 50;
+
+    create table mp_invoice (
+        version integer not null,
+        created_at timestamp(6) with time zone not null,
+        id bigint not null,
+        number varchar(20) not null,
+        primary key (id)
+    );
+
+    create table mp_receipt (
+        version integer not null,
+        created_at timestamp(6) with time zone not null,
+        id bigint not null,
+        note varchar(60),
+        primary key (id)
+    );