Fix Copilot declined-install warning newline - #14222

Fixes #14189

Description

When gh copilot cannot find Copilot CLI and installation is declined, its warning does not end with a newline. This leaves the next shell prompt on the same line.

Add a trailing newline to the warning and cover its exact output in the primary run-function table test.

While adding that coverage, consolidate the existing execution-failure test into the run-function table and move the telemetry sampling assertion into the constructor table. This keeps command-level behavior in the two primary table tests.

How did you test this change?

Given Copilot CLI was excluded from PATH, when I ran a locally built gh copilot in a terminal and declined installation, then the warning and following shell marker appeared on separate lines:

? GitHub Copilot CLI is not installed. Would you like to install it? No
! Copilot CLI was not installed
SHELL_PROMPT_MARKER

Key points

• The declined-install warning now terminates its output before returning.
• The existing execution-failure coverage is consolidated into the run-function table.
• The existing telemetry sampling assertion is consolidated into the constructor table.

Notes for reviewers

Start with the declined-install branch, then review its output case in the run-function table. Issue #14189 contains the original terminal reproduction.

Authorship and follow-up

Who wrote this:

• A human wrote it.
• An agent wrote it under close human direction.
• An agent wrote it independently, and no human has guided the implementation beyond the initial prompt.

Who answers review comments:

• @BagToad will read and reply directly.
• An agent will draft replies and @username will read them before they are posted.
• Nobody has explicitly committed to replying.