Test logging refactoring

[paulomorgado]

Summary

This updates test logging to remove reflection-based method name lookup and replaces the Serilog-based xUnit logging setup with MartinCostello.Logging.XUnit.

Part of #1434

Why

Using [CallerMemberName] is a better fit for test log messages and scopes than System.Reflection.MethodBase.GetCurrentMethod() because the compiler supplies the caller name directly. That avoids reflection overhead, removes nullable/reflection-specific handling, and keeps the code simpler while still producing the same method names in test output.

MartinCostello.Logging.XUnit is also a lighter-weight option for test logging. It plugs directly into Microsoft.Extensions.Logging and ITestOutputHelper, so the tests no longer need a full Serilog logger configuration plus xUnit and console sinks just to write test output. This reduces test-only dependencies and keeps logging setup focused on the xUnit test scenario.

Changes

• Added caller-member-name helpers for test method logging.
• Replaced reflection calls in test log messages and scopes.
• Switched affected test logger factories from Serilog to MartinCostello.Logging.XUnit.
• Updated test project package references to remove Serilog test logging packages.