Bump extern/fmt from ae1e93d to f5ec5ad (#589)

Bumps [extern/fmt](https://github.com/fmtlib/fmt) from `ae1e93d` to
`f5ec5ad`.
<details>
<summary>Commits</summary>
<ul>
<li><a
href="https://github.com/fmtlib/fmt/commit/f5ec5ada2bcb2c64306f3d8c25dd919dbbe4692e"><code>f5ec5ad</code></a>
Update syntax.rst</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/3b5f3de3b57505c7f1a60ee40ef3448c623b1326"><code>3b5f3de</code></a>
Make CMake version message less confusing (<a
href="https://github.com/fmtlib/fmt/issues/3907">#3907</a>)</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/ca9193983bdfa5cd3351d7801f31925f4dee8e2e"><code>ca91939</code></a>
Replace std::fill_n with fmt::detail::fill_n (<a
href="https://github.com/fmtlib/fmt/issues/3909">#3909</a>)</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/74a187288bbf10e2eb7bd6282715530392e8a2a2"><code>74a1872</code></a>
Implemented fmt::day, fmt::month, fmt::year and related unit tests (<a
href="https://github.com/fmtlib/fmt/issues/3906">#3906</a>)</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/88620e53a4ffe4cb02af02fc13d6618ff9727f94"><code>88620e5</code></a>
Range formatting documentation (<a
href="https://github.com/fmtlib/fmt/issues/3905">#3905</a>)</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/5d63e87d235b86341f8d87f79ed8eb9825f34c44"><code>5d63e87</code></a>
Add a formatter for float128</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/aecec01b34aa3d1bb3fb991d4f75b0750508f9a0"><code>aecec01</code></a>
Initial support for extended FP types</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/5af88653eb9c57940cecad748e1192de1a1a0bb3"><code>5af8865</code></a>
Cleanup</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/45b772f85c0c8ef95cdee73a2f33ed5d69739e28"><code>45b772f</code></a>
Improve std::complex formatter to be compatible with P2197R0 (<a
href="https://github.com/fmtlib/fmt/issues/3900">#3900</a>)</li>
<li><a
href="https://github.com/fmtlib/fmt/commit/53347891cf658c6ff02370f566c06376671551e2"><code>5334789</code></a>
Make line buffering test less flaky</li>
<li>Additional commits viewable in <a
href="https://github.com/fmtlib/fmt/compare/ae1e93d34de6caff6f318abdb06ff0db33a00792...f5ec5ada2bcb2c64306f3d8c25dd919dbbe4692e">compare
view</a></li>
</ul>
</details>
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