Add a PR build workflow (#78)

Obviously,
* you can't test GH actions locally
* and you can't test the actions in the repo without the actual source code
* and you don't want to include the actions with the initial source code commit if its _wrong_ 

So, here's the GH action to test this that we _think_ is right

.cargo/config.toml

@@ -1,6 +1,7 @@
 # -Ccontrol-flow-guard: Enable Control Flow Guard, needed for OneBranch's post-build analysis (https://learn.microsoft.com/en-us/cpp/build/reference/guard-enable-control-flow-guard).
 [target.'cfg(target_os = "windows")']
 rustflags = [
+    "-Dwarnings",
     "-Ccontrol-flow-guard",
     "-Ctarget-feature=+crt-static",
     "-Clink-args=/DEFAULTLIB:ucrt.lib /NODEFAULTLIB:vcruntime.lib /NODEFAULTLIB:msvcrt.lib /NODEFAULTLIB:libucrt.lib"

.github/actions/fix-environment/action.yml

@@ -0,0 +1,44 @@
+name: Fix environment
+description: GitHub VMs aren't configured correctly
+# Shamelessly borrowed from https://github.com/microsoft/windows-rs/blob/master/.github/actions/fix-environment/action.yml
+runs:
+  using: "composite"
+  steps:
+    - name: Configure environment
+      shell: pwsh
+      run: |
+        $vs_root = & "${env:ProgramFiles(x86)}\Microsoft Visual Studio\Installer\vswhere.exe" `
+          -latest -property installationPath -format value
+
+        switch -Wildcard ("${{ matrix.target }}")
+        {
+          "*-pc-windows-gnu"
+          {
+            "C:\msys64\mingw64\bin;C:\msys64\mingw32\bin" >> $env:GITHUB_PATH
+          }
+          "i686*"
+          {
+            "${env:ProgramFiles(x86)}\Windows Kits\10\bin\10.0.22000.0\x86" >> $env:GITHUB_PATH
+            ((Resolve-Path "$vs_root\VC\Tools\MSVC\*\bin\Hostx86\x86")
+              | Sort-Object -Descending | Select -First 1).ToString() >> $env:GITHUB_PATH
+          }
+          "x86_64*"
+          {
+            "${env:ProgramFiles(x86)}\Windows Kits\10\bin\10.0.22000.0\x64" >> $env:GITHUB_PATH
+            ((Resolve-Path "$vs_root\VC\Tools\MSVC\*\bin\Hostx64\x64")
+              | Sort-Object -Descending | Select -First 1).ToString() >> $env:GITHUB_PATH
+          }
+          "aarch64*"
+          {
+            "${env:ProgramFiles(x86)}\Windows Kits\10\bin\10.0.22000.0\x64" >> $env:GITHUB_PATH
+            ((Resolve-Path "$vs_root\VC\Tools\MSVC\*\bin\Hostx64\x64")
+              | Sort-Object -Descending | Select -First 1).ToString() >> $env:GITHUB_PATH
+          }
+          "*"
+          {
+            (Join-Path $env:GITHUB_WORKSPACE "target\debug\deps").ToString() >> $env:GITHUB_PATH
+            (Join-Path $env:GITHUB_WORKSPACE "target\test\debug\deps").ToString() >> $env:GITHUB_PATH
+            "INCLUDE=${env:ProgramFiles(x86)}\Windows Kits\10\include\10.0.22000.0\winrt;${env:ProgramFiles(x86)}\Windows Kits\10\include\10.0.22000.0\cppwinrt" `
+              >> $env:GITHUB_ENV
+          }
+        }

.github/workflows/pr-build.yaml

@@ -0,0 +1,52 @@
+name: PR Build & Test
+
+on:
+  pull_request:
+  push:
+    paths-ignore:
+      - '.github/ISSUE_TEMPLATE/**'
+    branches:
+      - main
+
+jobs:
+  check:
+    runs-on: windows-2022
+
+    strategy:
+      matrix:
+          # Apparently ARM targets aren't usable in GH actions
+          # target: [x86_64-pc-windows-msvc, i686-pc-windows-msvc, aarch64-pc-windows-msvc]
+          target: [x86_64-pc-windows-msvc, i686-pc-windows-msvc]
+          branding: [Inbox, Stable, Dev]
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v4
+
+      - name: Update toolchain
+        run: rustup update --no-self-update stable && rustup default stable-${{ matrix.target }}
+
+      - name: Add toolchain target
+        run: rustup target add ${{ matrix.target }}
+
+      - name: Install fmt
+        run: rustup component add rustfmt
+
+      - name: Install clippy
+        run: rustup component add clippy
+
+      - name: Fix environment
+        uses: ./.github/actions/fix-environment
+
+      - name: Clean
+        run:  cargo clean
+
+      - name: Run fmt
+        run: cargo fmt --all -- --check
+
+      # Test will build the code, then also test it.
+      - name: Test
+        run:  cargo test --no-default-features --features ${{matrix.branding}}  --target ${{ matrix.target }}
+
+      - name: Run clippy
+        run: cargo clippy --no-default-features --features ${{matrix.branding}} --target ${{matrix.target}} 2>&1