gh-118527: Intern filename, name, and qualname in code objects. (#118558)

This interns the strings for `co_filename`, `co_name`, and `co_qualname`
on codeobjects in the free-threaded build. This partially addresses a
reference counting bottleneck when creating closures concurrently. The
closures take the name and qualified name from the code object.

Author: colesbury

Diff for: Objects/codeobject.c

@@ -390,6 +390,11 @@ init_code(PyCodeObject *co, struct _PyCodeConstructor *con)
     co->co_filename = Py_NewRef(con->filename);
     co->co_name = Py_NewRef(con->name);
     co->co_qualname = Py_NewRef(con->qualname);
+#ifdef Py_GIL_DISABLED
+    PyUnicode_InternInPlace(&co->co_filename);
+    PyUnicode_InternInPlace(&co->co_name);
+    PyUnicode_InternInPlace(&co->co_qualname);
+#endif
     co->co_flags = con->flags;
 
     co->co_firstlineno = con->firstlineno;