Parallelise function space unit tests

### Are there any linked Issues or Pull Requests?

_No response_

### Brief description

Currently, function space unit tests are serial only. To fully test function spaces, their unit tests need to be run in parallel

### Further details of the issue.

The function space unit tests are already complicated as they consist of 44 parameterised tests that test different versions of the various function spaces defined within LFRic. These are all tested against canned data held in ``unit-test/support/fs_test_data_mod.F90``.

However, all these unit tests are serial, so testing what function spaces give for ``last_dof_owned``, ``last_dof_annexed``, ``last_dof_halo(n)`` and ``undf`` all return the same value. These are not very satisfactory tests.

The tests should be made to run in parallel with function spaces that describe data with proper annexed and halo dofs. Not only will this require some re-writing of the unit tests, but the data in ``unit-test/support/fs_test_data_mod.F90`` will have to be updated.

Start with the function space unit-test suite and read unit-test/support/fs_test_data_mod.F90, which contains the canned test data. Review how the 44 parameterised tests currently exercise last_dof_owned, last_dof_annexed, last_dof_halo(n) and undf in serial. Done means the tests run in parallel with proper annexed and halo dofs and the support data validates the resulting values.

Written by the indexing model from the issue text.