Recursive indexing of concatenated arrays

[jipolanco]

This is an attempt to fix the performance issues discussed in #132. These are type instability issues when indexing heterogeneous concatenated arrays with getindex and setindex!.

In this PR, getindex and setindex! are reimplemented for the Vcat{1}, Vcat{2} and Hcat lazy concatenation types.

Here is a small benchmark for comparison, on Julia 1.5.1:

using BenchmarkTools
using LazyArrays
using StaticArrays

A = Vcat(
    rand(1:10, 12),
    @SVector(zeros(Int, 4)),
    4:42,
)

N = length(A)

On LazyArrays master:

@btime $A[1];   # 7.356 ns (0 allocations: 0 bytes)
@btime $A[14];  # 43.875 ns (2 allocations: 112 bytes)
@btime $A[$N];  # 80.788 ns (4 allocations: 208 bytes)

With this PR:

@btime $A[1];   # 4.329 ns (0 allocations: 0 bytes)
@btime $A[14];  # 4.668 ns (0 allocations: 0 bytes)
@btime $A[$N];  # 6.105 ns (0 allocations: 0 bytes)

[codecov]

Codecov Report

Merging #133 into master will decrease coverage by 0.10%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #133      +/-   ##
==========================================
- Coverage   87.13%   87.03%   -0.11%     
==========================================
  Files          12       12              
  Lines        1360     1357       -3     
==========================================
- Hits         1185     1181       -4     
- Misses        175      176       +1     

Impacted Files	Coverage Δ
src/lazyconcat.jl	93.78% <100.00%> (-0.04%)	⬇️
src/lazyoperations.jl	77.45% <0.00%> (-0.99%)	⬇️

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[dlfivefifty]

Looks like just one line is missing in coverage, are you able to cover this? (Sometimes its just a bug in codecov and I can merge as is in that case.)

[jipolanco]

Sorry, I had left a function that in the end I didn't use. Should be good now.

[dlfivefifty]

If bump the patch version (to v0.17.7) I can merge and tag right away

[dlfivefifty]

Actually I'll just do the tag now