Add trailing stops for OrderFactory bracket orders

[hope2see]

Pull Request

This PR resolves the issue, which is to add trailing stop orders for OrderFactory bracket order.

Summary

• Added/modified factories.pxd/pyx to support trailing stops in bracket
• Modified emulator.pyx to solve the problem with trigger_price being None.
• Added test_exchange_bracket_trailing_stop_orders.py
• Modified trailing_stop_limit.pyx/pyx to refine small redundancies.

Related Issues/PRs

Issue#2523

Type of change

• Bug fix (non-breaking)
• [v] New feature (non-breaking)
• Breaking change (impacts existing behavior)
• [v] Documentation update
• [v] Maintenance / chore

Release notes

• I added a concise entry to RELEASES.md that follows the existing conventions (when applicable)

Testing

Ensure new or changed logic is covered by tests.

• Affected code paths are already covered by the test suite
• [v] I added/updated tests to cover new or changed logic

test_exchange_bracket_trailing_stop_orders.py

[cjdsellers]

Hi @hope2see,

Thanks so much for the work here!

I think the grouping of params by order type turned out well, it's quite intuitive to align with the leading prefixes tp_* and sl_* like you've done.

[cjdsellers]

Are you able to share your thinking behind this decision?

Is this because with an activation_price we don't expect there to be a trigger_price until the activation price is hit?

[hope2see]

Yes. Unless trigger_price can be given by users, it remains unset until the order is activated. Thus, it can't be guaranteed to be not None without checking the order's status.

Actually, the modification in emulator.pyx should have been made when the initial PR for adding activation_price was submitted. At that time, I hadn't tested emulation_trigger, so it was overlooked.
Now, emulation_trigger is covered in the newly added tests for bracket order.