Fix dpnp.linspace returning NaN for equal infinite endpoints (#3043)

`dpnp.linspace` returned `NaN` instead of the endpoint value when
`start` and `stop` are equal and infinite — e.g. `dpnp.linspace(inf,
inf, 4)` gave `[nan inf inf nan]`.

The bug had two independent sources:
- The array path in `dpnp_linspace` computed `delta = stop - start`, so
`inf - inf = NaN` propagated through the whole result.
- The scalar path delegates to `dpnp.tensor.linspace`, whose affine
kernel `LinearSequenceAffineFunctor` evaluates `start * w + stop * wc`;
at the endpoints one weight is `0`, and `inf * 0 = NaN`.

The PR proposes to fix all the places.

Note, the tests compare against NumPy on versions that include the fix
(NumPy >= 2.6.0) and fall back to explicit expected values on older
NumPy. 94dcfef

Author: github-actions[bot]

_modules/dpnp/dpnp_iface_arraycreation.html

@@ -3984,7 +3984,7 @@ <h1>Source code for dpnp.dpnp_iface_arraycreation</h1><div class="highlight"><pr
 <span class="sd">        There are `num` equally spaced samples in the closed interval</span>
 <span class="sd">        [`start`, `stop`] or the half-open interval [`start`, `stop`)</span>
 <span class="sd">        (depending on whether `endpoint` is ``True`` or ``False``).</span>
-<span class="sd">    step : float, optional</span>
+<span class="sd">    step : dpnp.ndarray, optional</span>
 <span class="sd">        Only returned if `retstep` is ``True``.</span>
 <span class="sd">        Size of spacing between samples.</span>
 

backend_doc/doxygen_crawl.html

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reference/comparison.html

@@ -1055,7 +1055,7 @@
 <h1>Comparison Table NumPy/ DPNP/ CuPy<a class="headerlink" href="#comparison-table-numpy-dpnp-cupy" title="Link to this heading">¶</a></h1>
 <p>Here is a list of NumPy and CuPy APIs and its corresponding DPNP implementations.</p>
 <p><code class="docutils literal notranslate"><span class="pre">-</span></code> in DPNP column means that DPNP implementation is not provided yet.</p>
-<p><strong>NumPy(v2.5.2) / DPNP(v0.21.0dev7+11.g1bfd8e6f6fe) / CuPy(v14.2.0) APIs</strong></p>
+<p><strong>NumPy(v2.5.2) / DPNP(v0.21.0dev7+13.g94dcfef845a) / CuPy(v14.2.0) APIs</strong></p>
 <section id="summary">
 <h2>Summary<a class="headerlink" href="#summary" title="Link to this heading">¶</a></h2>
 <div class="table-wrapper docutils container">

reference/generated/dpnp.linspace.html

@@ -1108,7 +1108,7 @@ <h1>dpnp.linspace<a class="headerlink" href="#dpnp-linspace" title="Link to this
 <li><p><strong>out</strong> (<em>dpnp.ndarray</em>) -- There are <cite>num</cite> equally spaced samples in the closed interval
 [<cite>start</cite>, <cite>stop</cite>] or the half-open interval [<cite>start</cite>, <cite>stop</cite>)
 (depending on whether <cite>endpoint</cite> is <code class="docutils literal notranslate"><span class="pre">True</span></code> or <code class="docutils literal notranslate"><span class="pre">False</span></code>).</p></li>
-<li><p><strong>step</strong> (<em>float, optional</em>) -- Only returned if <cite>retstep</cite> is <code class="docutils literal notranslate"><span class="pre">True</span></code>.
+<li><p><strong>step</strong> (<em>dpnp.ndarray, optional</em>) -- Only returned if <cite>retstep</cite> is <code class="docutils literal notranslate"><span class="pre">True</span></code>.
 Size of spacing between samples.</p></li>
 </ul>
 </p>