Respect custom strides in scalar compound assignment

[CAOShurong]

Checklist

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• Tests have been added for new features or bug fixes.
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Description

Fixes #2773.

Scalar compound assignment currently writes the storage prefix even when an adaptor has padded strides. Use logical iteration for non-dense strides, while preserving physical iteration for dense layouts, including custom axis permutations. Dense-layout traversal preserves the behavior of aliased scalars and stateful, noncopyable functors.

Tests cover padded rows and columns, empty adaptors, scalar aliasing and functor state for both dynamic- and fixed-rank adaptors.

Validation: 26 adaptor cases (114 assertions), installed CMake consumers, and 224 owned-buffer checks under AddressSanitizer passed. A partial broader run passed 1,219 cases from the 77 test modules that compile on MSVC 19.42; the full build encounters the same baseline errors in test_xfunction and test_xvectorize.

Local microbenchmarks found up to ~1.7 ns overhead for 16-element arrays; large-array candidate/baseline ratios reached 1.13x. Linux and macOS validation remains to CI.