multidict Free-Threading Analysis Report

I ran a free threading analysis tool on multidict and it found that:

> **Overall difficulty: Easy-Medium.** multidict is one of the *best-positioned* extensions for free-threading — all the hard structural work (multi-phase init, heap types, module state) is already done. What's missing is purely per-object synchronization, which is a mechanical addition of `Py_BEGIN_CRITICAL_SECTION` calls.

The full report is at https://gist.github.com/devdanzin/fa00e03ef041c030660f083116a7e1b6. It contains issue descriptions, suggested fixes, and reproducers for some of the issues.

I hope it helps.