Review for compatibility with Protocol 22 and .NET 9

[steven-tomlinson]

Protocol 22 for Stellar is in Testnet. It doesn't appear to have any breaking changes, but we should verify all operations are compatible.

Additionally, .NET 9 is now available https://learn.microsoft.com/en-us/dotnet/core/whats-new/dotnet-9/overview
Need to review for compatibility and update code-base to maintain currency.

[steven-tomlinson]

npgSQL is still behind .NET 9. Since the default configuration relies on PostgreSQL, we'll defer the upgrade to .NET 9.
In the meantime, I will push an interim release to bring all packages up to the latest .NET 8.x.x version.

Note: Developers using the Stellar DotNet Identity Framework with a different data provider can still update their projects and packages to .NET 9 without any issues.