Bump extern/fmt from 621e9c1 to c95722a (#759)

Bumps [extern/fmt](https://github.com/fmtlib/fmt) from `621e9c1` to
`c95722a`.
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/fmtlib/fmt/commit/c95722ad629092b7c5e8bcc4ce4019c413f53711"><code>c95722a</code></a>
Improve naming consistency</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/db06b0df875856968c562d564b595a4e2861144e"><code>db06b0d</code></a>
Use countl_zero in bigint</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/b9ec48d9ca60253ca295910e9078566090d98135"><code>b9ec48d</code></a>
Cleanup bigint</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/3faf6f181e4b277868578dd97034aada145aee8c"><code>3faf6f1</code></a>
Add min_of/max_of</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/d64b100a30f5e3df9f7fe08cfdf3d89ed755ad6d"><code>d64b100</code></a>
Relax constexpr</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/ff9ee0461a8dd02cbaf9458aa13301aa1099c0f7"><code>ff9ee04</code></a>
Fix handling FMT_BUILTIN_TYPES</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/1c5883bef081a5cce75bdc4dab0ce922d3bb600f"><code>1c5883b</code></a>
Test nondeterministic conversion to format string</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/cacc3108c5b74020dba7bf3c6d3a7e58cdc085b2"><code>cacc310</code></a>
Don't assume repeated evaluation of string literal produce the same
pointer</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/fade652ade6e9ba4b16e7484cbda5ee4c9178918"><code>fade652</code></a>
Require clang &gt;=15 for _BitInt support (<a
href="https://github.com/fmtlib/fmt/issues/4176">#4176</a>)</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/96dca569a1251ea77f434c2773d4db55c4b8a488"><code>96dca56</code></a>
Module linkage fixes for shared build (<a
href="https://github.com/fmtlib/fmt/issues/4169">#4169</a>)</li>
<li>Additional commits viewable in <a
href="https://github.com/fmtlib/fmt/compare/621e9c17c58ab7ee3ec0faf3ec39e3565332593f...c95722ad629092b7c5e8bcc4ce4019c413f53711">compare
view</a></li>
</ul>
</details>
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