fix: route push completion output through logger

[tomatotomata]

What changed

Registry.push() now routes its completion message through the existing logger instead of writing directly to stdout. It also accepts the documented quiet option, so callers such as examples/simple/push.py can suppress that message without a TypeError.

Why

The direct print() made it impossible to pipe a digest or other command output cleanly. This keeps informational output on the logger path and preserves the completion message by default.

Validation

• python -m pytest -p no:recording oras/tests/test_provider.py -k 'quiet_output or quiet_suppresses' -q passed: 2 tests
• python -m compileall -q oras passed
• python -m isort --check-only oras/provider.py oras/tests/test_provider.py passed
• git diff --check passed
• Full suite: 54 passed, 19 skipped, 1 unrelated baseline failure in test_sanitize_path caused by Windows path separator expectations

This addresses #229. I used an AI coding assistant during implementation and reviewed the resulting diff and test evidence locally.

[vsoch]

This looks good @tomatotomata - a simple and reasonable change. Please see the DCO requirements here: https://github.com/oras-project/oras-py/pull/249/checks?check_run_id=92784221176

[tomatotomata]

The DCO check was the only action-required gate. I amended the head commit with the authorized sign-off Signed-off-by: ahmad <ahmadalgaidy@hotmail.com> and force-pushed the same branch. The code and validation scope are unchanged, so the checks can rerun against the new head.