feat(csharp): add .net building and testing workflow, solution file (#879)

.github/workflows/dotnet.yml

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+# This workflow will build a .NET project
+# For more information see: https://docs.github.com/en/actions/automating-builds-and-tests/building-and-testing-net
+
+name: .NET
+
+on:
+  push:
+    branches: [ "main" ]
+    paths: ["codes/csharp/**/*.cs"]
+  pull_request:
+    branches: [ "main" ]
+    paths: ["codes/csharp/**/*.cs"]
+
+jobs:
+  build:
+    name: .NET ${{ matrix.dotnet-version }} on ${{ matrix.os }}
+    runs-on: ${{ matrix.os }}
+    defaults:
+      run:
+        working-directory: codes/csharp/
+    strategy:
+      matrix:
+        os: [ubuntu-latest, macos-latest, windows-latest]
+        dotnet-version: ["6.0.x"]
+
+    steps:
+    - uses: actions/checkout@v3
+
+    - name: Setup .NET ${{ matrix.dotnet-version }}
+      uses: actions/setup-dotnet@v3
+      with:
+        dotnet-version: ${{ matrix.dotnet-version }}
+    - name: Restore dependencies
+      run: dotnet restore hello-algo.csproj
+    - name: Build
+      run: dotnet build --no-restore hello-algo.csproj
+    - name: Test with dotnet
+      run: dotnet test hello-algo.csproj

codes/csharp/csharp.sln

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+
+Microsoft Visual Studio Solution File, Format Version 12.00
+# Visual Studio Version 17
+VisualStudioVersion = 17.5.002.0
+MinimumVisualStudioVersion = 10.0.40219.1
+Project("{9A19103F-16F7-4668-BE54-9A1E7A4F7556}") = "hello-algo", "hello-algo.csproj", "{48B60439-EFDC-4C8F-AE8D-41979958C8AC}"
+EndProject
+Global
+	GlobalSection(SolutionConfigurationPlatforms) = preSolution
+		Debug|Any CPU = Debug|Any CPU
+		Release|Any CPU = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(ProjectConfigurationPlatforms) = postSolution
+		{48B60439-EFDC-4C8F-AE8D-41979958C8AC}.Debug|Any CPU.ActiveCfg = Debug|Any CPU
+		{48B60439-EFDC-4C8F-AE8D-41979958C8AC}.Debug|Any CPU.Build.0 = Debug|Any CPU
+		{48B60439-EFDC-4C8F-AE8D-41979958C8AC}.Release|Any CPU.ActiveCfg = Release|Any CPU
+		{48B60439-EFDC-4C8F-AE8D-41979958C8AC}.Release|Any CPU.Build.0 = Release|Any CPU
+	EndGlobalSection
+	GlobalSection(SolutionProperties) = preSolution
+		HideSolutionNode = FALSE
+	EndGlobalSection
+	GlobalSection(ExtensibilityGlobals) = postSolution
+		SolutionGuid = {1E773F8A-FF66-4974-820B-FCE9032D19AE}
+	EndGlobalSection
+EndGlobal