GroupVerify 0.2.0: Steam group / override verification with an API for other plugins

Players are verified when they're in the configured Steam group (public memberslistxml,
refetched every 10 minutes, kept on failure) or have an unexpired override row in
gv_verified, written by the web panel. Settings and data live in CS2-SimpleAdmin's MySQL
database (gv_verified, gv_settings, gv_migrations), reached through its API.

- css_gv_group <groupId64|0>, css_gv_enable, css_gv_disable (@css/root): verification runs
  only when enabled with a group set.
- css_verify <target>: why a player is or isn't verified. Admin and above (by immunity from
  SimpleAdmin's groups) plus Guardian, unless admin_overrides.json says otherwise.
- groupverify:api (shared/GroupVerifyApi): IsVerified, GetStatus, IsActive and
  OnVerifiedChanged. The API object lives in the shared assembly, so it survives hot
  reloads of GroupVerify.

GroupVerifyApi/GroupVerifyApi.csproj

@@ -0,0 +1,20 @@
+<Project Sdk="Microsoft.NET.Sdk">
+  <!-- GroupVerify's API for other plugins. Installed in addons/counterstrikesharp/shared/GroupVerifyApi/,
+       never in a plugin's folder: CSS loads it once from there, so every plugin shares its types. -->
+  <PropertyGroup>
+    <TargetFramework>net10.0</TargetFramework>
+    <ImplicitUsings>enable</ImplicitUsings>
+    <Nullable>enable</Nullable>
+    <AssemblyName>GroupVerifyApi</AssemblyName>
+    <RootNamespace>GroupVerifyApi</RootNamespace>
+    <GenerateDocumentationFile>true</GenerateDocumentationFile>
+  </PropertyGroup>
+  <ItemGroup>
+    <!-- Compile-time only: the server already has CounterStrikeSharp.API.dll -->
+    <PackageReference Include="CounterStrikeSharp.API" Version="1.0.376">
+      <PrivateAssets>none</PrivateAssets>
+      <ExcludeAssets>runtime</ExcludeAssets>
+      <IncludeAssets>compile; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
+    </PackageReference>
+  </ItemGroup>
+</Project>