Preserve quoted shell arguments in run parsing

[biefan]

Summary

• replace naive whitespace splitting in parse_run_arguments() with shell-aware tokenization
• stop list-valued options at both long flags and the short -s strategies alias
• add regression coverage for quoted paths, quoted --memory-labels JSON, and -s after --initializers in pyrit shell

Problem

pyrit shell forwards the raw run ... line into parse_run_arguments(), which currently has two parsing edge cases:

1. It uses args_string.split(), which breaks any argument that relies on quotes to preserve spaces.
2. Its list-valued option loops only stop at --... flags, so the documented short alias -s can be swallowed into a preceding multi-value option like --initializers.

Examples that fail today:

• --initialization-scripts "/tmp/my script.py"
• --env-files "/tmp/dev env.env"
• --memory-labels '{"experiment": "test 1"}'\n- --initializers init1 -s s1 s2\n\nThose inputs are well-formed shell commands and should parse the same way as the equivalent long-form options.\n\n## Testing\n- .venv/bin/pytest tests/unit/cli/test_frontend_core.py -q\n- .venv/bin/pytest tests/unit/cli/test_pyrit_shell.py -q