Bug#1127800: fenics-dolfinx autopkgtest timeout with the nanobind 2.11.0 rebuild

[Drew Parsons]

Source: fenics-dolfinx
Followup-For: Bug #1127800

nanobind 2.11.0 has introduced pathologies, and there appear to be more than one of them.

nanobind 2.11.0 failure on 32-bit arches is reported in Bug#1127672

The amd64 log in testing at
https://ci.debian.net/packages/f/fenics-dolfinx/testing/amd64/68633180/
or unstable at
https://ci.debian.net/packages/f/fenics-dolfinx/unstable/amd64/68655583/
suggests one more separate problem.

There seems to be a pathology in the serial execution of MPI-parallel programs.
test-dolfinx-python-unittest starts at 919s, and the first python unit
tests (serial) reach test_vtkhdf.py at 2529s and finish at 2722s.
So that's 30 minutes test time, consistent with what we had before
(23 min)

The failing MPI python unit tests started at 4380s, reached
test_vtkhdf.py at 5314s (15 minutes, fine), then test_vtkhdf.py is
killed at 10916s, 1.5 hours on the one unit test, not so fine.


Then even worse, on my local machine, dolfinx does not finish importing at all in
reasonable time with serial `python3 -c "import dolfinx"`.
An MPI job runs "normally" even with 1 process,
`mpirun -n 1 python3 -c "import dolfinx"`