fix(component): roll back failed startup

[RerankerGuo]

Summary

Roll back partially started component lifecycles when BaseComponent.start() fails.

Problem

start() currently starts owned dependencies before invoking the parent's _start(). If the parent hook raises, the parent remains marked as not started, so a later close() returns immediately while the owned components remain running.

This can leak clients, tasks, or other resources created by default-factory dependencies.

Changes

• Track owned components that successfully started during the current attempt.
• If parent startup fails, invoke its cleanup hook and close started owned components in reverse order.
• Preserve the original startup exception even if rollback cleanup also fails.
• Add a regression test covering failed parent startup and defensive follow-up close.

Evidence

Before the fix:

FAILED test_start_failure_rolls_back_parent_and_owned_components
assert parent.close_count == 1
E assert 0 == 1

After the fix:

pytest tests/unit/test_base_component.py -q
25 passed

pytest tests/unit/test_job.py -q
21 passed

All relevant pre-commit hooks pass.

Scope

Successful startup and normal idempotent close behavior are unchanged.

[jinliyl]

LGTM