Redesigned dpnp.modf function to be a part of ufunc and vm pybind11 extensions

[antonwolfy]

The PR updates implementation of dpnp.modf to move it from old legacy backend to be part of ufunc and vm extensions.
Also DPNPUnaryTwoOutputsFunc class is extended with support of oneMKL VM functions.

The tests for unary functions with 2 output arrays are separated to dpnp/tests/test_unary_two_outputs_ufuncs.py file.
And the legacy implementation of dpnp.modf was cleaned up.

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[coveralls]

coverage: 81.458% (+0.06%) from 81.399%
when pulling 57e4b99 on impl-modf
into 03e0975 on master.

[github-actions]

View rendered docs @ https://intelpython.github.io/dpnp/pull/2654/index.html

[github-actions]

Array API standard conformance tests for dpnp=0.20.0dev0=py313h509198e_46 ran successfully.
Passed: 1227
Failed: 0
Skipped: 9