[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	2ea565f...	main / 2ea565f...
Constitutive models/Visco-elastic Ψ	0.049 ± 0.03 ms	0.0487 ± 0.029 ms	1.01 ± 0.86
Constitutive models/Visco-elastic ∂Ψu	0.0551 ± 0.004 ms	0.0547 ± 0.0021 ms	1.01 ± 0.083
Constitutive models/Visco-elastic ∂Ψuu	0.105 ± 0.025 ms	0.104 ± 0.018 ms	1.01 ± 0.29
Simulations/StaticMechanicalDirichlet	0.145 ± 0.0078 s	0.143 ± 0.011 s	1.01 ± 0.093
Simulations/StaticMechanicalNeumann	0.135 ± 0.01 s	0.136 ± 0.014 s	0.993 ± 0.12
Simulations/ViscoElastic	19.4 s	19 s	1.02
Tensor algebra/Cofactor	0.07 ± 0.01 μs	0.08 ± 0.01 μs	0.875 ± 0.17
Tensor algebra/Det(A)Inv(A')	0.121 ± 0.04 μs	0.13 ± 0.001 μs	0.931 ± 0.31
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	2.6 ± 0.023 s	2.55 ± 0.035 s	1.02 ± 0.016

Memory benchmarks

	main	2ea565f...	main / 2ea565f...
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: 0.093 GB	1.48 M allocs: 0.093 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