chore(deps): Update the FastPFOR C++ library to v0.3.1 (#62)

Currently, the build fails on macOS with this error. It seems something
is wrong with this version of FastPFOR's `cmake_modules/simde.cmake`.
Fortunately, it seems it's fixed in [the latest
release](https://github.com/fast-pack/FastPFOR/releases/tag/v0.3.1). So,
this pull request updates the C++ library.

(Honestly, I'm not sure what problem this is and why this works now. The
only change on the file was that specifying the commit hash of simde's
repository
(fast-pack/FastPFOR@f7771da))

```
  Building for architecture: arm64
  CMake Error at cmake_modules/simde.cmake:9 (add_library):
    add_library cannot create imported target "simde" because another target
    with the same name already exists.
  Call Stack (most recent call first):
    CMakeLists.txt:47 (include)
```

---------

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Yuri Astrakhan <YuriAstrakhan@gmail.com>

Author: 3 people

.github/workflows/ci.yml

@@ -13,16 +13,30 @@ defaults:
 
 jobs:
   test:
-    name: Test
-    runs-on: ubuntu-latest
+    name: Test on ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+    strategy:
+      fail-fast: true
+      matrix:
+        include:
+          - os: ubuntu-latest
+          - os: macos-latest
     steps:
       - uses: actions/checkout@v6
         with: { submodules: recursive }
       - if: github.event_name != 'release' && github.event_name != 'workflow_dispatch'
         uses: Swatinem/rust-cache@v2
       - uses: taiki-e/install-action@v2
         with: { tool: 'just,cargo-binstall' }
-      - run: just ci-test
+      - if: runner.os == 'macOS'
+        run: brew install simde
+      - if: runner.os == 'macOS'
+        run: just ci-test
+        env:
+          CXXFLAGS: -I/opt/homebrew/include
+          CFLAGS: -I/opt/homebrew/include
+      - if: runner.os == 'Linux'
+        run: just ci-test
 
   test-nightly:
     name: Nightly-specific tests