Fix reduction contig impl offset handling

[oleksandr-pavlyk]

This PR modifies computation of typed pointer to take offsets into account in reduction implementations for contiguous inputs.

It also adds tests which would fail before this change

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[github-actions]

View rendered docs @ https://intelpython.github.io/dpctl/pulls/1458/index.html

[coveralls]

coverage: 85.748%. remained the same when pulling bfba152 on fix-reduction-contig_impl-offset-handling into 03fd737 on master.

[github-actions]

Array API standard conformance tests for dpctl=0.15.1dev0=py310ha25a700_68 ran successfully.
Passed: 934
Failed: 66
Skipped: 119

[github-actions]

Array API standard conformance tests for dpctl=0.15.1dev0=py310ha25a700_69 ran successfully.
Passed: 935
Failed: 65
Skipped: 119

[github-actions]

Array API standard conformance tests for dpctl=0.15.1dev0=py310ha25a700_70 ran successfully.
Passed: 935
Failed: 65
Skipped: 119