fix(cli): expose tuist test run help

What changed

• Exposes the hidden tuist test run subcommand in the tuist help test subcommand list.
• Adds root tuist test help discussion pointing users to tuist help test run for execution options.
• Updates tuist test run discussion to clarify that tuist test --clean and tuist test run --clean are equivalent.

Why

Users looking at tuist help test could only see test-run inspection and management commands, even though the executable test options such as --clean, -d, and -T live on the default run subcommand. That made the command discoverability confusing.

Root cause

TestRunCommand was registered as the default subcommand for tuist test, but it also had shouldDisplay: false, so ArgumentParser omitted it from the root test help menu.

Impact

The existing shorthand invocation remains unchanged, while the help menu now points users toward the command that documents the test execution flags.

Validation

Not run locally. Per maintainer guidance for this small help metadata change, local compilation was intentionally skipped because the generated Xcode build is expensive for this worktree.