Don't cache TrivialInterlacer

[jishnub]

On master

julia> B = ApproxFunBase.interlacer(Fourier())
ApproxFunBase.BlockInterlacer((Ones(ℵ₀), Ones(ℵ₀)))

julia> @btime ApproxFunBase.cache($B)[1:100];
  19.937 μs (503 allocations: 40.66 KiB)

julia> f = Fun(Chebyshev(0..1) + Chebyshev(1..2))
Fun(Chebyshev(0..1) ⨄ Chebyshev(1..2), [0.5, 1.5, 0.5, 0.5])

julia> @btime Derivative() * $f;
  7.413 μs (128 allocations: 7.98 KiB)

This PR

julia> @btime ApproxFunBase.cache($B)[1:100];
  1.685 ns (0 allocations: 0 bytes)

julia> @btime Derivative() * $f;
  3.285 μs (60 allocations: 4.44 KiB)

[codecov]

Codecov Report

Patch coverage: 100.00% and project coverage change: +0.07% 🎉

Comparison is base (4f33475) 71.88% compared to head (e20c37d) 71.95%.
Report is 2 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #504      +/-   ##
==========================================
+ Coverage   71.88%   71.95%   +0.07%     
==========================================
  Files          81       81              
  Lines        8546     8569      +23     
==========================================
+ Hits         6143     6166      +23     
  Misses       2403     2403              

Files Changed	Coverage Δ
src/Operators/general/InterlaceOperator.jl	81.33% <ø> (ø)
src/LinearAlgebra/helper.jl	70.31% <100.00%> (+1.38%)	⬆️
src/Operators/banded/Conversion.jl	87.09% <100.00%> (+0.65%)	⬆️
src/eigen.jl	96.42% <100.00%> (ø)

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