Add grouped TPSL order example

[Hyrudotcom]

Summary

• Add a dedicated basic_grouped_tpsl.py example for grouped parent + take-profit + stop-loss orders.
• Build the three orders in one bulk_orders(..., grouping="normalTpsl") action.
• Cancel any resting orders by default, with --keep-open available when users want to inspect the orders on testnet.

Closes #86.

Validation

• PYTHONPYCACHEPREFIX=/private/tmp/codex-pycache python3 -m py_compile examples/basic_grouped_tpsl.py
• git diff --check HEAD~1 HEAD