UI: Migrate from backoff to backon - drop-in replacement, archived upstream

Type of issue: Feature request

Which image of the operator are you using? Not applicable (UI component issue).

Describe the problem:

The backoff library (litl/backoff) was archived in August 2025 and is no longer maintained. It is also incompatible with Python 3.14+ due to the removal of the deprecated asyncio.iscoroutinefunction() API.

The Postgres Operator UI currently depends on backoff==2.2.1 (pinned in ui/requirements.txt) and uses it in ui/operator_ui/main.py:

from backoff import expo, on_exception

@on_exception(expo, RequestException)
def get_target_namespace():
    ...

Describe the solution:

Migrate to backon — a modern, actively maintained evolution of backoff. It is a drop-in replacement: change only the import statement.

-from backoff import expo, on_exception
+from backon import expo, on_exception

-@on_exception(expo, RequestException)
+@on_exception(expo, RequestException)

The dependency change in ui/requirements.txt:

-backoff==2.2.1
+backon>=4.3.0

Why backon?

• Zero dependencies (pure Python, stdlib only)
• Same public API as backoff — on_exception, on_predicate, expo, fibo, constant, runtime
• Full type hints
• Python 3.10+ compatible (including 3.14+)
• Additional features if ever needed: circuit breaker, hedging, testing utilities, global toggle
• I am the author and happy to submit a PR

Additional context:

• backon PyPI: https://pypi.org/project/backon/
• backon GitHub: https://github.com/Llucs/backon
• Migration guide: https://github.com/Llucs/backon#migrating-from-backoff

Start with ui/requirements.txt and ui/operator_ui/main.py, where the current backoff dependency and retry decorator are named. Review the existing import and dependency constraint, then verify the UI still installs and the retry behavior remains compatible with Python 3.14+. Done means backoff is replaced by backon in both locations without changing the decorator behavior.