feat: update .NET SDK support to include versions 8.0, 9.0, and 10.0;…

[lukekim]

This pull request introduces significant improvements to the Spice.ai .NET SDK, focusing on enhanced multi-framework support, resource management, and developer usability. The most important changes include support for .NET 8, 9, and 10, proper disposal of network resources via IDisposable in key classes, stricter input validation, and updates to CI/CD workflows to build and test across multiple frameworks.

Multi-framework support and packaging:

• Updated Spice/Spice.csproj to support netstandard2.0, net8.0, net9.0, and net10.0, and upgraded package dependencies to the latest versions. Also changed the package ID to lowercase and bumped the version to 0.2.0.
• Updated CI/CD workflows (.github/workflows/pr.yaml, .github/workflows/publish.yaml) to build and test against multiple .NET versions (8, 9, 10) and improved NuGet publishing to skip duplicates. [1] [2]

Resource management and disposal:

• Implemented IDisposable in SpiceClient and SpiceFlightClient to ensure proper cleanup of gRPC channels and HTTP clients, preventing resource leaks. [1] [2] [3]
• Updated documentation and code samples in README.md to emphasize using using statements/declarations for automatic disposal of SpiceClient instances. [1] [2]

Input validation and error handling:

• Added stricter input validation to SpiceClientBuilder methods (WithFlightAddress, WithApiKey, WithMaxRetries, WithUserAgent) using ThrowHelper for pre-.NET 8 targets and built-in exceptions for .NET 8+. [1] [2] [3] [4] [5]
• Improved error messages and exception types for invalid API keys and other parameters.

Documentation and usability:

• Updated README.md to reflect new framework support, improved code samples to use using var, and added a section on memory management best practices. [1] [2] [3]

These changes collectively make the SDK more robust, easier to use, and compatible with the latest .NET platforms.