gh-127945: fix thread safety of creating instances of ctypes structures #131716
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ctypesthread safety auditing (and fixing) #127945In free-threading, concurrent mutations to StgInfo is not thread safe. Therefore to make it thread safe, when modifying StgInfo, this PR adds
STGINFO_LOCKandSTGINFO_UNLOCKmacros which are used to acquire critical section of the StgInfo. The critical section is write only and is acquired when modifying the StgInfo fields and while setting thedict_finalbit. Once thedict_finalis set, StgInfo is treated as read only and no further modifications are allowed. This allows to avoid acquiring the critical section for most read operations whendict_finalis set (general case).Fixes #128567
Fixes #128570