Add equals_layout hook for == on LayoutArrays

[dlfivefifty]

Adds a layout hook for equality, alongside mapreduce_layout and copyto!_layout:

equals_layout(_, _, A, B) = invoke(==, Tuple{AbstractArray,AbstractArray}, A, B)
equals_layout(A, B) = equals_layout(MemoryLayout(A), MemoryLayout(B), A, B)
==(A::LayoutArray, B::AbstractArray) = equals_layout(A, B)
# ... plus the mirrored and SubArray{<:Any,<:Any,<:LayoutArray} variants

== routes through the hook whenever either argument is a LayoutArray or a view of one. The default falls back to Base's generic AbstractArray comparison, so behaviour doesn't change unless a layout opts in. Layouts can then specialise equality, for example to compare structured data directly rather than entry by entry.

Notes

• The SubArray overloads don't constrain the dimension, so comparing views of different dimensions isn't ambiguous.
• The new methods are ambiguous with SparseArrays.ReadOnly's ==. ArrayLayoutsSparseArraysExt adds resolving methods, guarded by isdefined(SparseArrays, :ReadOnly).
• Test.detect_ambiguities over ArrayLayouts, Base, LinearAlgebra, FillArrays and SparseArrays reports no == ambiguities.
• Downstream packages that define ==(::AbstractArray, ::SomeType) or its mirror may see new ambiguities when one side is a LayoutArray.

Tests

A new == testset in test/test_layoutarray.jl covers comparisons in both directions between layout arrays, plain arrays and views. It also includes size mismatches and a custom layout that overloads equals_layout. The full test suite passes locally.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.33%. Comparing base (be85225) to head (3f26a0e).

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #284      +/-   ##
==========================================
+ Coverage   90.26%   90.33%   +0.06%     
==========================================
  Files          12       12              
  Lines        1973     1987      +14     
==========================================
+ Hits         1781     1795      +14     
  Misses        192      192              

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