tests: avoid shell parsing in CLI helper

[kuishou68]

Summary

• stop building a shell command string in tests/sherlock_interactives.py
• invoke the CLI helper via sys.executable -m sherlock_project with an argv list
• preserve stderr capture and the existing CalledProcessError -> InteractivesSubprocessError flow

Why

Using shell=True here makes the helper depend on shell parsing and quoting behavior instead of direct CLI argument handling. An argv-based call is safer, easier to reason about, and more faithful to how the tests want to exercise the CLI.

Self-review

• kept the change scoped to the interactive test helper only
• used shlex.split(...) so existing string-based test inputs still map onto argv cleanly
• used sys.executable to avoid relying on a separate sherlock or py shell command being present on PATH

Closes #2864