… 3.14

PYC_MAGIC_NUMBER changes from 2994 to 3627, matching CPython 3.14's
pyc_magic_number_token (0x0a0d0e2b). marshal FORMAT_VERSION drops from
5 to 4 (the encoder/marshal.version value; the decoder already accepts
both). check_pyc_magic_number_bytes now compares all four magic bytes
instead of the first two.

SourceFileLoader.get_code now also looks for .pyc files using
_RP_FALLBACK_CACHE_TAGS (currently ('cpython-314',)) in addition to
sys.implementation.cache_tag. The matched .pyc is only used for
reading; recompilation still writes to the RustPython-tagged path, so
CPython's .pyc is never overwritten. Source-stat / hash / timestamp
validation logic is unchanged.

CPython's marshal supports TYPE_SLICE from format version 4 onwards
and that is the default version. Rejecting slice dumps below version
5 made marshal.dumps(slice(...)) fail with the default version and
broke test.test_marshal.SliceTestCase.test_slice.

Lib/importlib/_bootstrap_external.py is CPython's own code copied
verbatim; local patches here defeat compatibility tracking. The
cpython-XX cache_tag fallback needs to live on the RustPython side
(Rust code or sys.implementation.cache_tag policy), not as edits to
the imported standard library.

This reverts commit 1fc426d0fb5fcdb50d35cad13bbb43e8f6ce1c7f.

Py_MARSHAL_VERSION is 5 in CPython 3.14.5 (Include/marshal.h:16) and
TYPE_SLICE serialization rejects version < 5 (Python/marshal.c:720).
Restore the same threshold and constant so marshal.version and the
slice-marshal gate match CPython.

Code objects embedded in const-tuples reset the depth budget on each
recursion, so a hostile or pathological marshal stream of code-in-tuple-
in-code can blow the stack despite MAX_MARSHAL_STACK_DEPTH. Pass the
current depth through deserialize_code_inner and read_marshal_const_tuple
and decrement at each code-object/tuple boundary.

Also route dict keys through deserialize_value_after_header so TYPE_CODE
keys decode instead of failing with BadType.

Rename CFG helpers and accessors to the names used in CPython's
compile.c (basicblock_next_instr, basicblock_last_instr,
basicblock_append_instructions, bb_has_fallthrough, is_jump,
make_cfg_traversal_stack, mark_warm/mark_cold, etc.). Drop the unused
boolop-folding gate, mark_cpython_cfg_label_block helper, and
ComprehensionLoopControl::iter_range field.

Track an is_coroutine flag on SymbolTable, set in async def, await, and
async comprehensions, and propagate it through non-generator
comprehensions per symtable_handle_comprehension().

Mark SetupCleanup/SetupFinally/SetupWith as has_arg pseudo-ops, mark
ForIter as a terminator, and add has_arg/has_const on AnyInstruction.
Fix Instruction::stack_effect_jump to delegate to the opcode's
stack_effect_jump rather than stack_effect.

- clippy: drop redundant `test_` prefix on three test functions and
  remove an unnecessary `u32` cast in basicblock_clear_reuses_cpython_spare_slots_in_offset_order
- insta: regenerate nested_double_async_with snapshot to match the new
  CFG output that drops unreferenced labels after the redundant-NOP pass
- regrtest: drop `@expectedFailure` markers from test_func_args,
  test_meth_args (test_compile), test_disassemble_with,
  test_disassemble_try_finally (test_dis), and test_except_star
  (test_monitoring) which now pass

The CPython invariant `assert(OPCODE_HAS_ARG(op) || !IS_BLOCK_PUSH(op))`
relies on SETUP_{FINALLY,CLEANUP,WITH} carrying `HAS_ARG_FLAG` in
CPython's metadata. The autogen tool reads pseudo-opcode properties from
target instructions and does not propagate the pseudo's own
HAS_ARG flag, so PseudoOpcode::has_arg() omits these three opcodes.
Drop the debug_assert that fired inside py_freeze proc-macro expansion.