Update QR tests to avoid element-wise comparisons

[vlad-perevezentsev]

This PR proposes updating QR tests to avoid direct element-wise comparisons which became unstable with oneMKL 2026.0 due to sign and phase differences in otherwise valid QR results

Since QR factorization is not unique, different MKL and NumPy versions may return results that differ by sign or complex phase while still representing a correct decomposition

To make the tests more stable this PR proposes using invariant-based validation for mode="raw" and mode="r" based on the unitarity of the Q factor (Q^H Q = I) and the resulting QR identity
R^H @ R = A^H @ A

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[github-actions]

Array API standard conformance tests for dpnp=0.20.0dev3=py313h509198e_11 ran successfully.
Passed: 1355
Failed: 2
Skipped: 16

[coveralls]

coverage: 81.124%. remained the same
when pulling 8cb6d29 on inskip_qr_tests
into e825de5 on master.

[github-actions]

View rendered docs @ https://intelpython.github.io/dpnp/pull/2785/index.html