Follow up the fix implemented in gh-2530 to fix dpnp.unique with axis=0 and 1d input

[antonwolfy]

The PR improves the fix implemented in dpnp.unique for axis=0 and 1d input.
Also it adds an explicit validation in case of floating axis passed.

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• Have you added a test, reproducer or referred to an issue with a reproducer?
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• Have you made sure that new changes do not introduce compiler warnings?
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[github-actions]

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

[github-actions]

Array API standard conformance tests for dpnp=0.19.0dev4=py313h509198e_10 ran successfully.
Passed: 1227
Failed: 0
Skipped: 9

[coveralls]

coverage: 71.779% (-0.001%) from 71.78%
when pulling b33aa5e on follow-up-gh-2530
into b27a7ca on master.

[vlad-perevezentsev]

LGTM
Thank you @antonwolfy