Add skill locations support to Copilot CLI session options and service (#4098)

* Add skill locations support to Copilot CLI session options and service

* Fix tests

* Add MockSkillLocations to CopilotCLISessionService for enhanced testing

* oops

* oops

* More Revert

* Apply suggestion from @Copilot

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

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Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>