New Features/API

HPy headers are C++ compliant
Python 3.10 support
HPyField: References to Python objects that can be stored in raw native memory owned by Python objects.
- new API functions: HPyField_Load, HPyField_Store
HPyGlobal: References to Python objects that can be stored into a C global variable.
- new API functions: HPyGlobal_Load, HPyGlobal_Store
- note: HPyGlobal does not allow to share Python objects between (sub)interpreters
GIL support
- new API functions: HPy_ReenterPythonExecution, HPy_LeavePythonExecution
Value building support (HPy_BuildValue)
New type slots
- HPy_mp_ass_subscript, HPy_mp_length, HPy_mp_subscript
- HPy_tp_finalize
Other new API functions
- HPyErr_SetFromErrnoWithFilename, HPyErr_SetFromErrnoWithFilenameObjects
- HPyErr_ExceptionMatches
- HPyErr_WarnEx
- HPyErr_WriteUnraisable
- HPy_Contains
- HPyLong_AsVoidPtr
- HPyLong_AsDouble
- HPyUnicode_AsASCIIString, HPyUnicode_DecodeASCII
- HPyUnicode_AsLatin1String, HPyUnicode_DecodeLatin1
- HPyUnicode_DecodeFSDefault, HPyUnicode_DecodeFSDefaultAndSize
- HPyUnicode_ReadChar

Debug mode

Support activation of debug mode via environment variable HPY_DEBUG
Support capturing stack traces of handle allocations
Check for invalid use of raw data pointers (e.g HPyUnicode_AsUTF8AndSize) after handle was closed.
Detect invalid handles returned from extension functions
Detect incorrect closing of handles passed as arguments

Removed unnecessary prefix "m_" from fields of HPyModuleDef (incompatible change)
For HPy implementors: new pytest mark for HPy tests assuming synchronous GC