cext: add Python 3.10 support * Replace "Py_TYPE(obj) = type;" with "Py_SET_TYPE(obj, type);" * Add pythoncapi_compat.h header file to get Py_SET_TYPE() on Python 2.7-3.8. Header file added to mercurial/ and contrib/python-zstandard/zstd/common/. In Python 3.10, Py_TYPE(obj) must not longer be used as an l-value. pythoncapi_compat.h comes from: https://github.com/pythoncapi/pythoncapi_compat Differential Revision: https://phab.mercurial-scm.org/D9825

revlog: decouple caching from addrevision callback for addgroup For changesets, it is useful to cache the content as it will almost always be processed afterwards. For manifests on the other hand, the content is often not used directly as there is a fast path for deltas. Explicitly disable the cache in exchangev2's manifest handling for that reason. Differential Revision: https://phab.mercurial-scm.org/D9847