Fix h.Vector[0] : TypeError: type 'hoc.Vector' is not subscriptable

[nrnhines]

Closes #2860

PyType_FromMetaClass resolves the issue but requires python version >= 3.12. The function is wrapped by
nrn_type_from_metaclass in nrn_metaclass.cpp and for python version < 3.12 it contains a "cursed" implementation that seems to work but required some tweaking on my part.

[x] In particular <3.12 seems to be missing the __module__ field. E.g we would like to see

$ python
Python 3.12.4 (main, Aug  5 2024, 09:04:16) [GCC 13.2.0] on linux
>>> from neuron import h
>>> v = h.Vector()
>>> type(v).__module__
'hoc'

Otherwise, for the most part, things are looking pretty good...

$ python
Python 3.10.14 (main, Jul 14 2024, 15:28:18) [GCC 13.2.0] on linux
>>> from neuron import h
>>> v = h.Vector(range(5))
>>> v.printf()
0	1	2	3	4	

5
>>> type(v)
<class 'hoc.Vector'>
>>> type(type(v))
<class 'hoc.HocClass'>
>>> type(type(type(v)))
<class 'type'>
>>> v
Vector[0]
>>> h.Vector[0][2]
2.0
>>> type(v)[0] == v
True
>>> type(v).mro()
[<class 'hoc.Vector'>, <class 'hoc.HocObject'>, <class 'object'>]

[x] Perhaps test/hoctests/tests/test_hoc_class_instance.py should be augmented with more extensive tests.

[x] At the moment, the implementation of hocclass_getitem is not very efficient. It may be worthwhile to give that object a Symbol* field (filled in at construction time) for immediate searching of sym->u.ctemplate->olist

[x] It is not clear at the moment that hocobject_type needs the custom_hocclass metaclass.

[ ] Should user defined hoc classes participate in this PR? Their type is old style...

>>> h('''
... begintemplate A
... endtemplate A
... ''')
True
>>> a = h.A()
>>> a
A[0]
>>> a == h.A[0]
True
>>> type(a)
<class 'hoc.HocObject'>

[ ] The nrnpy_hoc.cpp implementation is somewhat unclean. Error handling is inconsistent in nrnpy_hoc()

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[codecov]

Codecov Report

Attention: Patch coverage is 76.74419% with 20 lines in your changes missing coverage. Please review.

Project coverage is 67.27%. Comparing base (8e3de33) to head (47212cc).

Files with missing lines	Patch %	Lines
src/nrnpython/nrnpy_hoc.cpp	65.95%	16 Missing ⚠️
src/nrnpython/nrn_metaclass.cpp	89.74%	4 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #2862   +/-   ##
=======================================
  Coverage   67.26%   67.27%           
=======================================
  Files         571      572    +1     
  Lines      104867   104943   +76     
=======================================
+ Hits        70542    70596   +54     
- Misses      34325    34347   +22     

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[1uc]

One small comment:

• the PR mixes NULL and nullptr.

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[bbpbuildbot]

Logfiles from GitLab pipeline #230716 (:white_check_mark:) 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
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• ✅ test:neuron:nmodl:nvhpc:omp

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Quality Gate passed

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