Modifies αr to be passed as a Reference

[jmartfrut]

Changes the Magnetic struct to accept αr as a Ref{Float64}.

This allows for external modification of the αr parameter, enabling dynamic adjustments and simplifying parameter updates without reconstructing the entire Magnetic object.

[github-actions]

Benchmark Results (Julia v1)

Time benchmarks

	main	cb6d1b9...	main / cb6d1b9...
Constitutive models/Visco-elastic Ψ	0.0471 ± 0.028 ms	0.0467 ± 0.027 ms	1.01 ± 0.83
Constitutive models/Visco-elastic ∂Ψu	0.0613 ± 0.0032 ms	0.0613 ± 0.0032 ms	1 ± 0.074
Constitutive models/Visco-elastic ∂Ψuu	0.109 ± 0.015 ms	0.109 ± 0.015 ms	1 ± 0.19
Simulations/ViscoElastic	0.0456 h	0.046 h	0.992
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	2.46 ± 0.013 s	2.48 ± 0.024 s	0.993 ± 0.011

Memory benchmarks

	main	cb6d1b9...	main / cb6d1b9...
Constitutive models/Visco-elastic Ψ	1.24 k allocs: 0.0782 MB	1.24 k allocs: 0.0782 MB	1
Constitutive models/Visco-elastic ∂Ψu	1.36 k allocs: 0.0904 MB	1.36 k allocs: 0.0904 MB	1
Constitutive models/Visco-elastic ∂Ψuu	2.31 k allocs: 0.155 MB	2.31 k allocs: 0.155 MB	1
Simulations/ViscoElastic	2.72 G allocs: 192 GB	2.72 G allocs: 192 GB	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