gh-115999: Specialize LOAD_SUPER_ATTR in free-threaded builds (gh-127128)

Use existing helpers to atomically modify the bytecode.  Add unit tests
to ensure specializing is happening as expected.  Add test_specialize.py
that can be used with ThreadSanitizer to detect data races.  
Fix thread safety issue with cell_set_contents().

Python/generated_cases.c.h

@@ -6330,7 +6330,7 @@
                 global_super_st = stack_pointer[-3];
                 uint16_t counter = read_u16(&this_instr[1].cache);
                 (void)counter;
-                #if ENABLE_SPECIALIZATION
+                #if ENABLE_SPECIALIZATION_FT
                 int load_method = oparg & 1;
                 if (ADAPTIVE_COUNTER_TRIGGERS(counter)) {
                     next_instr = this_instr;
@@ -6341,7 +6341,7 @@
                 }
                 OPCODE_DEFERRED_INC(LOAD_SUPER_ATTR);
                 ADVANCE_ADAPTIVE_COUNTER(this_instr[1].counter);
-                #endif  /* ENABLE_SPECIALIZATION */
+                #endif  /* ENABLE_SPECIALIZATION_FT */
             }
             // _LOAD_SUPER_ATTR
             {