arrow

ARROW-10519: [Python] Fix deadlock when importing pandas from several threads

Fix a lock ordering-induced deadlock between the Python GIL
and the `std::once_flag` lock used in `arrow::py::internal::InitPandasStaticData`.

Thread A:
* takes the GIL
* calls `arrow::py::internal::InitPandasStaticData`
  * which calls `std::call_once`, which acquires the lock inside the `std::once_flag`
    * which imports the `pandas` module
      * which releases the GIL before reading the code object from disk
      * and then tries to re-acquire the GIL

Thread B:
* takes the GIL
* calls `arrow::py::internal::InitPandasStaticData`
  * which calls `std::call_once`, which tries to acquire the lock inside the `std::once_flag`

Closes #8615 from pitrou/ARROW-10519-pandas-import-deadlock

Authored-by: Antoine Pitrou <antoine@python.org>
Signed-off-by: Antoine Pitrou <antoine@python.org>