Require values for shell list arguments

[biefan]

Summary

• require at least one value for list-style pyrit_shell run arguments
• prevent empty-value flags from silently degrading into empty lists or fallback behavior
• add regression coverage for all list-style shell run flags

Problem

Several list-style run arguments currently accept zero values:

• --initializers
• --initialization-scripts
• --env-files
• --strategies / -s
• --dataset-names

When that happens, parse_run_arguments() returns an empty list and keeps parsing the rest of the command.

That creates silent misconfiguration paths such as:

• run demo --initializers --max-retries 2
• run demo --env-files --database InMemory
• run demo --dataset-names --max-dataset-size 5

In shell mode this is especially misleading because the command is accepted even though the user explicitly provided an incomplete flag.

Testing

• .venv/bin/pytest tests/unit/cli/test_frontend_core.py -q
• .venv/bin/pytest tests/unit/cli/test_pyrit_shell.py -q -k parse_error