Acquire gil for the full scope of the lifetime returned matrix

[bakpaul]

In the binding, what is expected from the overloaded funciton is an array that'll be copied. If the gil is released too early the structure can be cleaned before the end of it use. So doing this make sure the structure is kept alive all along. It actually solved a segfault on the following example when launched with runSofa

import Sofa
import numpy as np


class PyForceField(Sofa.Core.ForceFieldVec3d):
    def __init__(self, *args, **kwargs):
        Sofa.Core.ForceFieldVec3d.__init__(self, *args, **kwargs)

    def addForce(self, mechanical_parameters, out_force, position, velocity):
        print("addForce()")

    def addDForce(self, mechanical_parameters, df, dx):
        print("addDForce()")

    def addKToMatrix(self, mechanical_parameters, n_particles, n_dimensions):
        print("addKToMatrix()")
        n_dofs = n_particles * n_dimensions
        return np.zeros((n_dofs, n_dofs, 1))


def createScene(root):
    plugins = root.addChild("Plugins")
    plugins.addObject("RequiredPlugin", pluginName=[
        "Sofa.Component.LinearSolver.Direct",  # Needed to use components [SparseLDLSolver]
        "Sofa.Component.ODESolver.Backward",  # Needed to use components [EulerImplicitSolver]
        "Sofa.Component.StateContainer",  # Needed to use components [MechanicalObject]
        "Sofa.Component.Visual",  # Needed to use components [VisualStyle]
        "Sofa.Component.Mass",
    ])

    root.addObject("VisualStyle")
    root.addObject("DefaultAnimationLoop", bbox=((-2, -2, -2), (2, 2, 2)))

    physics = root.addChild("Physics")
    physics.addObject("EulerImplicitSolver")
    physics.addObject("SparseLDLSolver", template="CompressedRowSparseMatrixd")
    physics.addObject("MechanicalObject", template="Vec3d", position=(0, 0, 0), showObject="true", drawMode="1", showObjectScale="0.1")
    # physics.addObject("UniformMass", name="mass", totalMass=1)
    physics.addObject(PyForceField())