The path toward a no-GIL Python

The Python Steering Council has posted adetailed plan for the addition of "free-threaded" (no globalinterpreter lock) support into the Python mainline. It will not be a shortprocess and does not have a guaranteed successful outcome.

Phase I: Experimental phase, which can start immediately, in whichthe free-threaded build is enabled through a build-timeoption. This should not be the default install anywhere. At leastone major Python release should include this experimentalfree-threaded build, to allow third-party packages to test and dotheir own experimentation. In this stage we should make it clearthe build is experimental, not supported for production use", andmay be reverted.