Updates αr to be mutable in HardMagnetic2D

[jmartfrut]

Changes the αr field in the HardMagnetic2D struct to be a Ref{Float64}.

This allows modification of the αr parameter after the object's construction, improving flexibility in simulations where this parameter needs to be dynamically adjusted. It also updates the access to αr to dereference the Ref object.

[github-actions]

Benchmark Results (Julia v1)

Time benchmarks

	main	d29630b...	main / d29630b...
Constitutive models/Visco-elastic Ψ	0.0486 ± 0.027 ms	0.0491 ± 0.028 ms	0.99 ± 0.79
Constitutive models/Visco-elastic ∂Ψu	0.0634 ± 0.0043 ms	0.0635 ± 0.004 ms	0.999 ± 0.092
Constitutive models/Visco-elastic ∂Ψuu	0.112 ± 0.014 ms	0.113 ± 0.015 ms	0.989 ± 0.18
Simulations/StaticMechanicalDirichlet	0.131 ± 0.0064 s	0.133 ± 0.0082 s	0.981 ± 0.077
Simulations/StaticMechanicalNeumann	0.127 ± 0.011 s	0.127 ± 0.011 s	0.997 ± 0.12
Simulations/ViscoElastic	20.3 s	20.6 s	0.985
Tensor algebra/Cofactor	0.07 ± 0.01 μs	0.07 ± 0.01 μs	1 ± 0.2
Tensor algebra/Det(A)Inv(A')	0.13 ± 0.001 μs	0.131 ± 0.01 μs	0.992 ± 0.076
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	2.41 ± 0.0095 s	2.4 ± 0.0094 s	1 ± 0.0056

Memory benchmarks

	main	d29630b...	main / d29630b...
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	1.36 k allocs: 0.0898 MB	1.36 k allocs: 0.0898 MB	1
Constitutive models/Visco-elastic ∂Ψuu	2.32 k allocs: 0.155 MB	2.32 k allocs: 0.155 MB	1
Simulations/StaticMechanicalDirichlet	1.51 M allocs: 0.109 GB	1.51 M allocs: 0.109 GB	1
Simulations/StaticMechanicalNeumann	1.48 M allocs: 0.0933 GB	1.48 M allocs: 0.0933 GB	1
Simulations/ViscoElastic	0.343 G allocs: 22 GB	0.343 G allocs: 22 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