* Fix data race all_type_info_populate in free-threading mode
Description:
- fixed data race all_type_info_populate in free-threading mode
- added test

For example, we have 2 threads entering `all_type_info`.
Both enter `all_type_info_get_cache`` function and
there is a first one which inserts a tuple (type, empty_vector) to the map
and second is waiting. Inserting thread gets the (iter_to_key, True) and non-inserting thread
after waiting gets (iter_to_key, False).
Inserting thread than will add a weakref and will then call into `all_type_info_populate`.
However, non-inserting thread is not entering `if (ins.second) {` clause and
returns `ins.first->second;`` which is just empty_vector.
Finally, non-inserting thread is failing the check in `allocate_layout`:
```c++
if (n_types == 0) {
    pybind11_fail(
        "instance allocation failed: new instance has no pybind11-registered base types");
}
```

* style: pre-commit fixes

* Addressed PR comments

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