Move tensor tests from dpctl

[vlad-perevezentsev]

This PR moves all tensor-related tests to dpnp/tests/tensor as part of the ongoing migration of tensor functionality from dpctl to dpnp.tensor

Key changes:

• Relocated 89 tensor tests (elementwise functions, usm_ndarray, and tensor utilities)
• Updated imports to use dpnp.tensor
• Included tests in packaging configuration
• Integrated tensor tests into CI
• Fixed several issues discovered during migration (dtype expectations, boolean reductions, etc.)
• Fixed a circular import in _usmarray.py
• Added SKIP_TENSOR_TESTS env variable to manage the launch of the test scope

In a follow-up PR:

• Conditional logic will be added to run dpctl_ext/tests only when changes affect the tensor code.
• Array API tests for tensor will be introduced and executed as a separate CI job.

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• Have you added your changes to the changelog?

[antonwolfy]

In general, LGTM

[antonwolfy]

Thank you @vlad-perevezentsev, no more comments from me