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Support 'nuc' norm in dpnp.linalg.cond (#3084)

This PR adds the nuclear norm (`"nuc"`) to the set of norms accepted by
`dpnp.linalg.cond`, aligning its supported `p` values with
`dpnp.linalg.norm` and with NumPy.

For `"nuc"` the condition number is computed through the existing
inverse-based branch as `norm(x, "nuc") * norm(inv(x), "nuc")`, i.e. the
product of the sums of the singular values of `x` and `inv(x)`. This
path was already functional (`dpnp.linalg.norm` supports `"nuc"` for
matrices), so no change to the computation itself is required — the
result matches NumPy for non-singular, batched, complex, boolean, empty,
and strided inputs.

Consistent with the other inverse-based norms (`1`, `-1`, `inf`, `-inf`,
`"fro"`), `dpnp.linalg.cond` raises `LinAlgError` on singular input when
`p="nuc"`, because `dpnp.linalg.inv` raises on singular matrices rather
than filling the result with `inf` the way NumPy does.

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