We have run out of flags bits in `PyTypeObject`'s `tp_flags`

PyTypeObject's tp_flags field is defined as an unsigned long. In effect this means that we have only 32 bits we can use for flags. We have already used all 32 of them.

Bits 15 and 16 are reserved for Stackless Python. Since Stackless Python is pining for the fjords, we could recycle those two bits. However that's not going to last long with likely changes necessary for parallelism and performance.

Any change to PyTypeObject breaks both API and ABI, but that's OK because:

• Adding a field or changing the size of a field is a backwards compatible API change.
• The existence of PyTypeObject is part of the stable ABI, but its layout is not.

The cleanest change, IMO, is to change unsigned long tp_flags to uint64_t tp_flags which gives us another 32 bits, which should last many more years.

まず PyTypeObject の定義と、その tp_flags フィールドのすべての使用箇所を確認し、提示された API および ABI の制約に照らして、提案された幅の変更を評価します。利用可能な flag ビットを拡張するための合意された設計に到達して実装し、影響を受けるインターフェースと互換性の動作に対処できれば完了です。