refactor: build Diagonal copies via map_diagonal

`map_diagonal(f, src)` is exactly `diagonal(f.(diagview(src)))`, so the
three `copy_input` methods can use it instead of constructing a `Diagonal`
directly. This keeps them consistent with the rest of the package, which
routes diagonal construction through `diagonal` rather than the
`LinearAlgebra` type.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: lkdvos

src/implementations/logarithm.jl

@@ -3,7 +3,7 @@
 function copy_input(::typeof(logarithm), A::AbstractMatrix)
     return copy!(similar(A, float(eltype(A))), A)
 end
-copy_input(::typeof(logarithm), A::Diagonal) = Diagonal(float.(diagview(A)))
+copy_input(::typeof(logarithm), A::Diagonal) = map_diagonal(float, A)
 
 function check_input(::typeof(logarithm!), A::AbstractMatrix, logA, alg::AbstractAlgorithm)
     m = LinearAlgebra.checksquare(A)

src/implementations/power.jl

@@ -3,7 +3,7 @@
 function copy_input(::typeof(power), A::AbstractMatrix, p::Real)
     return copy!(similar(A, float(eltype(A))), A), p
 end
-copy_input(::typeof(power), A::Diagonal, p::Real) = Diagonal(float.(diagview(A))), p
+copy_input(::typeof(power), A::Diagonal, p::Real) = map_diagonal(float, A), p
 
 function check_input(::typeof(power!), A::AbstractMatrix, p::Real, powA, alg::AbstractAlgorithm)
     m = LinearAlgebra.checksquare(A)

src/implementations/squareroot.jl

@@ -3,7 +3,7 @@
 function copy_input(::typeof(squareroot), A::AbstractMatrix)
     return copy!(similar(A, float(eltype(A))), A)
 end
-copy_input(::typeof(squareroot), A::Diagonal) = Diagonal(float.(diagview(A)))
+copy_input(::typeof(squareroot), A::Diagonal) = map_diagonal(float, A)
 
 function check_input(::typeof(squareroot!), A::AbstractMatrix, sqrtA, alg::AbstractAlgorithm)
     m = LinearAlgebra.checksquare(A)