[$] A per-interpreter GIL

"Subinterpreters", which are separate Python interpreters running in thesame process that can becreated usingthe C API, have been a part of Python since the previous century(version1.5 in1997), but they are largely unknown and unused.Eric Snow has been on something of a quest, since 2015 or so, to bring better multicore processing to Python byway of subinterpreters (or "multiple interpreters"). He has made it partof the way there, with the adoption of a separate global interpreter lock (GIL) for eachsubinterpreter, whichwas added for Python3.12. Back in April, Snow gave a talk (YouTube video) atPyCon about multiple interpreters, their status, and his plans for thefeature in the future.