Fix complex matrix assignment ownership

[fallintoplace]

Summary

• make copy assignment release the previous allocation through copy-and-swap
• make move assignment safely transfer ownership through swap, including self-move
• mark move construction and assignment noexcept
• cover repeated assignments across empty and differently sized matrices, self-copy, and self-move

Both assignment operators previously overwrote an owning pointer without releasing its allocation. Aliasing the source made the behavior worse: self-copy discarded the original values, while self-move nulled its own pointer.

Testing

• pre-commit run --files runtime/cudaq/operators/matrix.h unittests/utils/Matrix.cpp
• macOS Apple Clang ASan+UBSan harness: 10,000 repeated copy/move assignments and self-assignment checks
• macOS leaks: 0 leaks

[copy-pr-bot]

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[1tnguyen]

/ok to test fd0616d

Command Bot: Processing...

[1tnguyen]

Overall, LGTM 👍 Thanks for the contribution @fallintoplace

[github-actions]

CI Summary (push) — ✅ passed

Run #29260722704 · ✅ 6 · ⏩ 7 · ❌ 0 · ⛔ 0

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[sacpis]

/ok to test 889822d

Command Bot: Processing...

[schweitzpgi]

Suggested change

	using std::swap;
	swap(dimensions, other.dimensions);
	swap(data, other.data);
	swap(internal_order, other.internal_order);
	std::swap(dimensions, other.dimensions);
	std::swap(data, other.data);
	std::swap(internal_order, other.internal_order);

[schweitzpgi]

It's weird to me that this doesn't use swap but copy assignment builds a temporary so that it can use swap instead of a simple deallocation.