[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	3b1212c...	main / 3b1212c...
Constitutive models/Visco-elastic Ψ	0.0564 ± 0.034 ms	0.0555 ± 0.034 ms	1.02 ± 0.87
Constitutive models/Visco-elastic ∂Ψu	0.0619 ± 0.012 ms	0.0609 ± 0.0033 ms	1.02 ± 0.2
Constitutive models/Visco-elastic ∂Ψuu	0.113 ± 0.034 ms	0.113 ± 0.02 ms	1.01 ± 0.35
Simulations/StaticMechanicalDirichlet	0.143 ± 0.01 s	0.144 ± 0.011 s	0.998 ± 0.1
Simulations/StaticMechanicalNeumann	0.124 ± 0.017 s	0.124 ± 0.021 s	0.997 ± 0.22
Simulations/ViscoElastic	21 s	21.4 s	0.982
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	0.12 ± 0.02 μs	0.925 ± 0.18
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	2.94 ± 0.038 s	3.09 ± 0.047 s	0.952 ± 0.019

Memory benchmarks

	main	3b1212c...	main / 3b1212c...
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