[FEATURE] Use file-scoped namespace on sample code

[AndrewKeepCoding]

Is your feature request related to a problem? Please describe.

Sample.xaml.cs uses block-scoped namespace slightly losing a bit of readability, also losing consistency because GenAIModel.cs uses file-scoped namespace.

Describe the solution you'd like

It'd be better Sample.xaml.cs uses file-scoped namespace.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context

There are other sample code that also uses block-scoped namespace.

[AndrewKeepCoding]

I could create a PR for these sample code.

[nmetulev]

Thanks Andrew - please feel free to submit a PR and update the samples - this is a good suggestion - thank you