Build: Bump cython from 3.1.5 to 3.1.6 (#2666)

Bumps [cython](https://github.com/cython/cython) from 3.1.5 to 3.1.6.
<details>
<summary>Changelog</summary>
<p><em>Sourced from <a
href="https://github.com/cython/cython/blob/master/CHANGES.rst">cython's
changelog</a>.</em></p>
<blockquote>
<h1>3.1.6 (2025-10-23)</h1>
<h2>Bugs fixed</h2>
<ul>
<li>
<p>Unicode characters formatted from C integers with
<code>f&quot;{value:c}&quot;</code> could result in
invalid Python string objects since Cython 3.1.0.
(Github issue :issue:<code>7240</code>)</p>
</li>
<li>
<p><code>cythonize</code> (program and function) now uses
<code>concurrent.futures.ProcessPoolExecutor</code>
instead of <code>multiprocessing.Pool</code> to fix a hang on build
failures in parallel builds.
A possible work-around is to disable parallel builds.
Patch by Sviatoslav Sydorenko. (Github issue
:issue:<code>7183</code>)</p>
</li>
</ul>
</blockquote>
</details>
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/cython/cython/commit/b40c676a7396e3b8ca25974bd5ca4b5cef7f9908"><code>b40c676</code></a>
Prepare release of 3.1.6.</li>
<li><a
href="https://github.com/cython/cython/commit/2c003320ea74b04ed28993cf048149b1046df260"><code>2c00332</code></a>
Build: Clear &quot;license-files&quot; option in setup metadata due
to</li>
<li><a
href="https://github.com/cython/cython/commit/6d0b9bd0879839ed9d2b06898d096441750751dc"><code>6d0b9bd</code></a>
Build: Use twine to check the wheels before uploading them.</li>
<li><a
href="https://github.com/cython/cython/commit/fecd0e5a2b76a7d540bc6a7119f6638d8ea87d2d"><code>fecd0e5</code></a>
Silence a C coercion warning in a test.</li>
<li><a
href="https://github.com/cython/cython/commit/2a68bbca81a3621d4b8a457e98a64a0391c02a09"><code>2a68bbc</code></a>
Avoid back-and-forth between signed and unsigned index types in C array
conve...</li>
<li><a
href="https://github.com/cython/cython/commit/18249752c95cffce9bf8383ee1c711accc4ee013"><code>1824975</code></a>
Silence a C compiler warning about implicit signed/unsigned
conversion.</li>
<li><a
href="https://github.com/cython/cython/commit/a583bc3cd0e779efd8e3db5a6caa6b2e6789ba8b"><code>a583bc3</code></a>
Disable parallelism in <code>cythonize</code> command/function on
<code>spawn</code> (<a
href="https://redirect.github.com/cython/cython/issues/7183">GH-7183</a>)</li>
<li><a
href="https://github.com/cython/cython/commit/2ee0bc1f047849e840326ff2ebddb9009ef6891b"><code>2ee0bc1</code></a>
Update changelog.</li>
<li><a
href="https://github.com/cython/cython/commit/b0f7b40f68d75815bf3c494f11cf58369e118880"><code>b0f7b40</code></a>
Fix f-string joining when non-ASCII &quot;{intvalue:c}&quot; character
formats are invo...</li>
<li><a
href="https://github.com/cython/cython/commit/67351ba379626aaeff3865071ccae3e649a96430"><code>67351ba</code></a>
Adapt release date of 3.1.5 to PyPI release time.</li>
<li>Additional commits viewable in <a
href="https://github.com/cython/cython/compare/3.1.5...3.1.6">compare
view</a></li>
</ul>
</details>
<br />


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Author: dependabot[bot]