chore: add CSharpier formatting

.github/workflows/format.yml

@@ -0,0 +1,30 @@
+name: Formatting
+
+on:
+  pull_request:
+  push:
+    branches:
+      - master
+  workflow_dispatch:
+
+jobs:
+  format:
+    name: Check formatting
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+
+      - name: Setup .NET
+        uses: actions/setup-dotnet@v5
+        with:
+          dotnet-version: 10.0.x
+
+      - name: Install CSharpier
+        run: dotnet tool install --tool-path ./.tools CSharpier --version 1.2.6
+
+      - name: Check formatting
+        run: |
+          mapfile -t files < <(git ls-files '*.cs' '*.csx' '*.csproj' '*.props' '*.targets' '*.xml' '*.slnx')
+          ./.tools/csharpier check "${files[@]}"

CONTRIBUTING.md

@@ -0,0 +1,29 @@
+# Contributing
+
+## Formatting
+
+Format C# files, XML project/configuration files, and `.slnx` files with
+CSharpier before opening a pull request.
+
+Install CSharpier as a local .NET tool:
+
+```sh
+dotnet tool install --global CSharpier
+```
+
+Format the checked files locally:
+
+```sh
+dotnet csharpier format $(git ls-files '*.cs' '*.csx' '*.csproj' '*.props' '*.targets' '*.xml' '*.slnx')
+```
+
+Check formatting without writing changes:
+
+```sh
+dotnet csharpier check $(git ls-files '*.cs' '*.csx' '*.csproj' '*.props' '*.targets' '*.xml' '*.slnx')
+```
+
+See the official CSharpier docs for
+[installation](https://csharpier.com/docs/About) and
+[editor integration](https://csharpier.com/docs/Editors), including format on
+save.

Directory.Build.props

@@ -1,5 +1,5 @@
 <Project>
   <PropertyGroup>
-    <TargetFrameworks>net8.0;net10.0</TargetFrameworks>
+    <TargetFrameworks>net10.0</TargetFrameworks>
   </PropertyGroup>
 </Project>

Directory.Packages.props

@@ -4,7 +4,11 @@
     <CentralPackageTransitivePinningEnabled>false</CentralPackageTransitivePinningEnabled>
   </PropertyGroup>
   <ItemGroup>
-    <PackageVersion Include="Microsoft.Extensions.DependencyModel" Version="2.1.0" />
+    <PackageVersion Include="CSharpier.Core" Version="1.2.6" />
+    <PackageVersion
+      Include="Microsoft.Extensions.DependencyModel"
+      Version="2.1.0"
+    />
     <PackageVersion Include="Microsoft.NET.Test.Sdk" Version="15.7.2" />
     <PackageVersion Include="MsgPack.Cli" Version="0.9.2" />
     <PackageVersion Include="MSTest.TestAdapter" Version="1.3.0" />