Extend _tensor_elementwise_impl (unary) part 2

[vlad-perevezentsev]

This PR extends _tensor_elementwise_impl with part of the unary functions:

cos,
cosh,
exp,
expm1,
floor,
imag,
isfinite,
isinf,
isnan,
log,
log1p,
log2,
log10,
logical_not,
negative,
positive,

• Have you provided a meaningful PR description?
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• Have you tested your changes locally for CPU and GPU devices?
• Have you made sure that new changes do not introduce compiler warnings?
• Have you checked performance impact of proposed changes?
• Have you added documentation for your changes, if necessary?
• Have you added your changes to the changelog?

[github-actions]

View rendered docs @ https://intelpython.github.io/dpnp/pull/2796/index.html

[ndgrigorian]

I looked over includes and nothing stood out, this one LGTM