should_simplify when using Template Expression

[Moelf]

I think conceptually it should be possible to do should_simplify inside each component of the Template Expression, maybe I should open an issue to track that?

Originally posted by @Moelf in #381

Currently, the option should_simplify seems to have no effect when using Template Expression, which results in HoF containing:

using SymbolicRegression, Distributions, Random, MLJ

toy_range = 20:300

toy_fun(x) = (12*x^2 + 2*x) ^ (0.1*log(x))

Random.seed!(87462)
X = (; xs = float.(toy_range))
true_ys = toy_fun.(X.xs)
# ys = @. true_ys * ( 1 + randn()/10);


structure = TemplateStructure{(:B, :E)}(
    ((; B, E), (x,)) -> B(x)^E(log(x))
)

model2 = SRRegressor(
    binary_operators=[+, *],
    expression_spec=TemplateExpressionSpec(; structure),
    should_simplify=true,
    should_optimize_constants=true,
    niterations=200
)
sr_mach2 = machine(model2, X, true_ys)

fit!(sr_mach2)

Below, in Complexity 12, B = ((#1 * 0.0062979) + #1) + 0.047125 should be simplified furthuer

Complexity  Loss       Score      Equation
2           6.628e+04  1.802e+01  ╭ B = #1
                                  ╰ E = 1.3458
4           2.277e+02  2.837e+00  ╭ B = #1 * 0.091314
                                  ╰ E = 2.3902
6           3.800e-04  6.652e+00  ╭ B = #1 * 3.4747
                                  ╰ E = #1 * 0.19992
8           2.626e-07  3.639e+00  ╭ B = #1 + 0.059995
                                  ╰ E = (#1 * 0.19999) + 0.24853
12          1.542e-08  7.088e-01  ╭ B = ((#1 * 0.0062979) + #1) + 0.047125
                                  ╰ E = (#1 * 0.20003) + 0.2468