Shaw: Python 3.13 gets a JIT

Traditionally CPython uses pretty chunky operations, but that is not very convenient for any sort of optimisation, so recent work has been on lowering to what they call a "tier-2" bytecode, which is more amenable to the sort of optimisations that parent comment calls for. Naturally, this makes interpretation (much) slower, and this JIT seems to reclaim some of the performance.