gh-145857: Replace DELETE_GLOBAL with PUSH_NULL; STORE_GLOBAL

Changes:
- Removed `DELETE_GLOBAL` opcode
- Allowed `STORE_GLOBAL` to take a `NULL` value corresponding to
  deletion
- Added test to `test_compiler_codegen.py`

Author: bkap123

Doc/library/dis.rst

@@ -1092,11 +1092,6 @@ iterations of the loop.
    Works as :opcode:`STORE_NAME`, but stores the name as a global.
 
 
-.. opcode:: DELETE_GLOBAL (namei)
-
-   Works as :opcode:`DELETE_NAME`, but deletes a global name.
-
-
 .. opcode:: LOAD_CONST (consti)
 
    Pushes ``co_consts[consti]`` onto the stack.

Include/internal/pycore_magic_number.h

@@ -294,6 +294,7 @@ Known values:
     Python 3.15a4 3661 (Lazy imports IMPORT_NAME opcode changes)
     Python 3.15a8 3662 (Add counter to RESUME)
     Python 3.15a8 3663 (Merge GET_ITER and GET_YIELD_FROM_ITER. Modify SEND to make it a bit more like FOR_ITER)
+    Python 3.15a8 3664 (Replace DELETE_GLOBAL with PUSH_NULL; STORE_GLOBAL)
 
 
     Python 3.16 will start with 3700
@@ -307,7 +308,7 @@ PC/launcher.c must also be updated.
 
 */
 
-#define PYC_MAGIC_NUMBER 3663
+#define PYC_MAGIC_NUMBER 3664
 /* This is equivalent to converting PYC_MAGIC_NUMBER to 2 bytes
    (little-endian) and then appending b'\r\n'. */
 #define PYC_MAGIC_NUMBER_TOKEN \