Restrict internal access and update test dependencies

Removed the `InternalsVisibleTo` attribute from `AssemblyInfo.cs`, restricting access to internal members for `FlowCtl.UnitTests`.

Cleaned up unused `using` directives in `InstallPluginCommandOptionsHandlerTests.cs` and added new dependencies for `FlowCtl.Core.Services.Authentication`, `FlowCtl.Core.Services.Logger`, and `FlowSynx.Client` namespaces to support updated functionality.

#127

Author: ziagham

src/FlowCtl/Properties/AssemblyInfo.cs

@@ -1,8 +1,4 @@
-using System;
-using System.Collections.Generic;
-using System.Threading;
-using System.Threading.Tasks;
-using FlowCtl.Commands.Plugins.Install;
+using FlowCtl.Commands.Plugins.Install;
 using FlowCtl.Core.Services.Authentication;
 using FlowCtl.Core.Services.Logger;
 using FlowSynx.Client;