test(python): add parity suites for builtins, strings, and scripts

[chaliy]

Summary

• replace the thin builtin and string parity shims with dedicated Python binding suites
• expand the script category with Node-style real-world Bash and BashTool scenarios while keeping existing high-level coverage
• add explicit async coverage in each category and verify the new acceptance-count targets locally

Testing

• ./.venv312/bin/ruff check tests/test_builtins.py tests/test_strings_and_quoting.py tests/test_scripts.py
• ./.venv312/bin/ruff format --check tests/test_builtins.py tests/test_strings_and_quoting.py tests/test_scripts.py
• ./.venv312/bin/pytest tests/test_builtins.py tests/test_strings_and_quoting.py tests/test_scripts.py -q

Closes #1260