Encapsulating benchmark inside bunction

[miguelmaso]

Same than #24. Attempting to fix #23

Moved all the benchmark into a single function.

#23 is failing due to a negative exponentiation (see log in https://github.com/MultiSimOLab/HyperFEM/actions/runs/18370871925/job/52333581834?pr=23)

[github-actions]

Benchmark Results (Julia v1)

Time benchmarks

	main	398c73a...	main / 398c73a...
Constitutive models/Visco-elastic Ψ	0.0489 ± 0.029 ms	0.0485 ± 0.029 ms	1.01 ± 0.85
Constitutive models/Visco-elastic ∂Ψu	0.0618 ± 0.0027 ms	0.0621 ± 0.0025 ms	0.994 ± 0.059
Constitutive models/Visco-elastic ∂Ψuu	0.111 ± 0.03 ms	0.112 ± 0.019 ms	0.993 ± 0.32
Simulations/ViscoElastic	28.3 s	28.2 s	1
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	2.59 ± 0.032 s	2.55 ± 0.014 s	1.02 ± 0.014

Memory benchmarks

	main	398c73a...	main / 398c73a...
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	0.392 G allocs: 31.1 GB	0.392 G allocs: 31.1 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	0.151 k allocs: 11.5 kB	0.151 k allocs: 11.5 kB	1