Fix OneElement multiplication with array elements

[jishnub]

After this,

julia> using FillArrays, StaticArrays, LinearAlgebra

julia> A = [SMatrix{2,3}(1:6)*(i+j) for i in 1:3, j in 1:2]
3×2 Matrix{SMatrix{2, 3, Int64, 6}}:
 [2 6 10; 4 8 12]    [3 9 15; 6 12 18]
 [3 9 15; 6 12 18]   [4 12 20; 8 16 24]
 [4 12 20; 8 16 24]  [5 15 25; 10 20 30]

julia> B = OneElement(SMatrix{3,2}(1:6), (2,2), (2,4))
2×4 OneElement{SMatrix{3, 2, Int64, 6}, 2, Tuple{Int64, Int64}, Tuple{Base.OneTo{Int64}, Base.OneTo{Int64}}}:
        ⋅                ⋅                ⋅                ⋅       
        ⋅         [1 4; 2 5; 3 6]         ⋅                ⋅       

julia> C = [SMatrix{2,2}(1:4) for i in 1:size(A,1), j in 1:4]
3×4 Matrix{SMatrix{2, 2, Int64, 4}}:
 [1 3; 2 4]  [1 3; 2 4]  [1 3; 2 4]  [1 3; 2 4]
 [1 3; 2 4]  [1 3; 2 4]  [1 3; 2 4]  [1 3; 2 4]
 [1 3; 2 4]  [1 3; 2 4]  [1 3; 2 4]  [1 3; 2 4]

julia> mul!(copy(C), A, B, 1, 2) == A * B + 2C
true

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (99278fa) 99.90% compared to head (0d76191) 99.90%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #335      +/-   ##
==========================================
- Coverage   99.90%   99.90%   -0.01%     
==========================================
  Files           8        8              
  Lines        1037     1034       -3     
==========================================
- Hits         1036     1033       -3     
  Misses          1        1              

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[jishnub]

Gentle bump. The main change here is to use Ref around the elements to treat them as scalars in broadcasting