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

[Llucs]

Is your feature request related to a problem? Please describe.

The backoff library (litl/backoff) was archived in August 2025 and is no longer maintained.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.

Censys Python currently depends on backoff >=2.0.0,<3.0.0 and uses it in censys/common/base.py:

• @backoff.on_exception(backoff.expo, ...) for retrying on server/timeout errors
• @backoff.on_predicate(backoff.runtime, ...) for Retry-After header handling

Describe the solution you would like

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

- import backoff
+ import backon
- @backoff.on_exception(backoff.expo, ...)
+ @backon.on_exception(backon.expo, ...)

Migration is trivial — the public API (on_exception, on_predicate, expo, runtime, max_tries, max_time, etc.) is identical. The pyproject.toml dependency would change from:

backoff = ">=2.0.0,<3.0.0"

to:

backon = ">=4.3.0"

Describe alternatives you have considered

• tenacity — popular but requires significantly more code changes (different API).
• python-backoff — a community fork that keeps the same API but does not add new features and still relies on the deprecated asyncio.iscoroutinefunction().
• Staying on backoff — the library is archived and will eventually break on newer Python versions.

backon is the only option that provides identical API compatibility with zero code changes beyond imports, plus it adds features like circuit breakers, hedging, testing utilities, and full type hints.

Additional context

• backon PyPI: https://pypi.org/project/backon/
• backon GitHub: https://github.com/Llucs/backon
• backon has zero dependencies and supports Python 3.10+
• I am the author of backon and happy to help with the migration if needed.