[NOT TO MERGE] Refactor Electro and ThermoElectro models

[miguelmaso]

WIP

model.electro() will replace the function _getCoupling(obj.electro, obj.mechano)

[github-actions]

Benchmark Results (Julia v1)

Time benchmarks

	main	b8ace66...	main / b8ace66...
Constitutive models/Visco-elastic Ψ	0.0524 ± 0.035 ms	0.0526 ± 0.034 ms	0.996 ± 0.92
Constitutive models/Visco-elastic ∂Ψu	0.0584 ± 0.002 ms	0.0585 ± 0.0019 ms	0.998 ± 0.047
Constitutive models/Visco-elastic ∂Ψuu	0.107 ± 0.014 ms	0.107 ± 0.014 ms	0.999 ± 0.18
Simulations/StaticMechanicalDirichlet	0.133 ± 0.0083 s	0.134 ± 0.0097 s	0.997 ± 0.095
Simulations/StaticMechanicalNeumann	0.126 ± 0.015 s	0.119 ± 0.016 s	1.06 ± 0.19
Simulations/ViscoElastic	19.4 s	19.6 s	0.99
Tensor algebra/Cofactor	0.07 ± 0.01 μs	0.07 ± 0.01 μs	1 ± 0.2
Tensor algebra/Det(A)Inv(A')	0.111 ± 0.01 μs	0.14 ± 0.011 μs	0.793 ± 0.095
Tensor algebra/δδ_λ_2d	30 ± 0 ns	30 ± 0 ns	1 ± 0
Tensor algebra/δδ_μ_2d	30 ± 0 ns	30 ± 0 ns	1 ± 0
time_to_load	2.74 ± 0.012 s	2.74 ± 0.0066 s	1 ± 0.0051

Memory benchmarks

	main	b8ace66...	main / b8ace66...
Constitutive models/Visco-elastic Ψ	1.24 k allocs: 0.0777 MB	1.24 k allocs: 0.0777 MB	1
Constitutive models/Visco-elastic ∂Ψu	1.29 k allocs: 0.0826 MB	1.29 k allocs: 0.0826 MB	1
Constitutive models/Visco-elastic ∂Ψuu	2.25 k allocs: 0.149 MB	2.25 k allocs: 0.149 MB	1
Simulations/StaticMechanicalDirichlet	1.51 M allocs: 0.108 GB	1.51 M allocs: 0.108 GB	1
Simulations/StaticMechanicalNeumann	1.48 M allocs: 0.0931 GB	1.48 M allocs: 0.0931 GB	1
Simulations/ViscoElastic	0.327 G allocs: 20.6 GB	0.327 G allocs: 20.6 GB	1
Tensor algebra/Cofactor	1 allocs: 0.0781 kB	1 allocs: 0.0781 kB	1
Tensor algebra/Det(A)Inv(A')	4 allocs: 0.25 kB	4 allocs: 0.25 kB	1
Tensor algebra/δδ_λ_2d	0 allocs: 0 B	0 allocs: 0 B
Tensor algebra/δδ_μ_2d	0 allocs: 0 B	0 allocs: 0 B
time_to_load	0.149 k allocs: 11.1 kB	0.149 k allocs: 11.1 kB	1