aspire run test coverage

[mitchdenny]

This PR introduces test coverage for the aspire run command. Here is a summary of the changes:

1. Introduces the IAppHostBackchannel interface so we can mock out backchannel behavior. There is a reusable test implementation of this that should allow us to simulate any behaviors we want.
2. Changed ConnectAsync(...) so it no longer takes a process, it wasn't using it.
3. Injects IAnsiConsole as a dependency to RunCommand. This is temporary as eventually the direct usage that RunCommand has on the ansi console will move into IInteractonService but I didn't want to tackle that in this PR. This was necessary to avoid some threading issues in the unit tests (seen that issue before in other areas with Spectre Console).
4. Added an explicit catch for OperationCancelledException. We were incorrectly returning error code 1 when the user did CTRL-C (writing the tests picked this up).
5. Relocated some of the existing test services since they are used in multiple places.
6. Copilot added some negative test cases for simple arg validation scenarios.
7. Added a end to end success test (which is fully mocked out so it should run quick).