Add test using mcna.mod

[olupton]

Originally motivated by BlueBrain/mod2c#92.

mcna.mod, which was already included in NEURON, showed the same issue when compiled for CoreNEURON.
This mechanism was not used in any NEURON tests, but it was used in a test from nrntest that is deleted from there in neuronsimulator/nrntest#30 and reimplemented in Python in this PR.

Unfortunately this MOD file does not compile when translated for CoreNEURON with NMODL (the original issue was using mod2c, but that is now deprecated). Fixing CoreNEURON + NMODL execution of this test is the subject of a follow-up ticket: #2397. Note that this use of PROTECT with GLOBAL variables is documented: https://nrn.readthedocs.io/en/latest/hoc/modelspec/programmatic/mechanisms/nmodl2.html#protect.

Also make some other improvements to tests and test helpers, generally in the direction of ensuring that tests do not leak changes to global NEURON state that cause other tests to fail:

• The coreneuron class/module (from neuron import coreneuron) can now be used as a context manager:

from neuron import coreneuron
with coreneuron(gpu=True, cell_permute=2):
  assert coreneuron.gpu
  assert coreneuron.cell_permute == 2
# old values are restored here

Finally, reorganise the pytest-based tests slightly:

• the old pynrn test group is renamed to pytest_coreneuron: MOD files under test/pytest_coreneuron are built for CoreNEURON and test_*.py files are executed using pytest
• a new pytest group is added: MOD files under test/pytest are only built for NEURON, but pytest is still used to execute test_*.py files

and simplify the fast_imem test a bit.

TODO:

• Merge Remove mcna tests that have moved to NEURON nrntest#30 and update "submodule" commit.
• Open follow-up issue for NMODL transpilation issues and CoreNEURON global variable issues --> NMODL cannot translate mcna.mod, CoreNEURON does not handle GLOBAL variables correctly #2397

[codecov]

Codecov Report

Merging #2308 (7e576ce) into master (7197b37) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2308      +/-   ##
==========================================
+ Coverage   60.18%   60.20%   +0.02%     
==========================================
  Files         627      627              
  Lines      121007   121062      +55     
==========================================
+ Hits        72827    72887      +60     
+ Misses      48180    48175       -5     

Impacted Files	Coverage Δ
share/lib/python/neuron/coreneuron.py	82.19% <100.00%> (+3.15%)	⬆️
share/lib/python/neuron/rxd/nodelist.py	66.66% <100.00%> (+9.21%)	⬆️
share/lib/python/neuron/tests/utils/__init__.py	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes

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[alexsavulescu]

LGTM to merge once TODOs done

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[azure-pipelines]

✔️ 7e576ce -> Azure artifacts URL

[bbpbuildbot]

Logfiles from GitLab pipeline #133975 (:no_entry:) have been uploaded here!

Status and direct links:

• ✅ mac_m1_cmake_build: [cmake, ON, OFF, OFF, address]
• ✅ spack_setup
• ✅ build:nmodl
• ✅ build:neuron:nmodl:intel:legacy
• ✅ build:neuron:nmodl:intel:shared
• ✅ build:neuron:nmodl:nvhpc:acc:legacy
• ✅ build:neuron:nmodl:nvhpc:acc:shared
• ✅ build:neuron:nmodl:nvhpc:omp:legacy
• ✅ build:neuron:nmodl:nvhpc:omp
• ✅ test:neuron:nmodl:intel:legacy
• ✅ test:neuron:nmodl:intel:shared
• ✅ test:neuron:nmodl:nvhpc:acc:legacy
• ✅ test:neuron:nmodl:nvhpc:acc:shared
• ✅ test:neuron:nmodl:nvhpc:omp:legacy
• ✅ test:neuron:nmodl:nvhpc:omp