Upgrade ASP.NET Projects to .NET 9/10 and Modernize Infrastructure

[aniket-okta]

Overview

This PR modernizes the okta-aspnet SDK to support the latest .NET versions and implements best practices for .NET development.

Changes

.NET Version Upgrades

• ✅ Upgraded .NET Framework target from 4.8 to 4.8.1
• ✅ Removed end-of-life .NET framework versions (net461, net472, netcoreapp3.1, net5.0)
• ✅ Added comprehensive .NET 9 and .NET 10 support across all projects

Package Updates

• ✅ Updated all NuGet packages to their latest stable versions
• ✅ Updated Microsoft.AspNetCore.* packages to latest versions
• ✅ Updated testing frameworks and dependencies

Code Quality Improvements

• ✅ Fixed safe code analysis warnings to improve code quality
• ✅ Addressed compiler warnings and suggestions

Build & Infrastructure

• ✅ Modernized ASP.NET Core test infrastructure
• ✅ Fixed strong name signing: switched from DelaySign to PublicSign for proper assembly signing

Benefits

• Support for latest .NET versions (9 & 10)
• Improved security with latest package versions
• Better code quality with resolved warnings
• Modern build and test infrastructure
• Proper strong name signing configuration

Testing

All existing tests continue to pass with the updated frameworks and packages.