Change default overage policy from REJECT to ALLOW_IF_AVAILABLE

[amavashev]

Summary

This PR changes the default overage policy for the @cycles decorator from REJECT to ALLOW_IF_AVAILABLE, making the library more permissive by default when actual usage exceeds the estimated budget at commit time.

Changes

• Updated DEFAULT_OVERAGE_POLICY constant from "REJECT" to "ALLOW_IF_AVAILABLE" in _constants.py
• Updated the default parameter value in the @cycles decorator function signature in decorator.py
• Updated the DecoratorConfig dataclass default in lifecycle.py
• Updated documentation in README.md and docstrings to reflect the new default behavior

Behavior Impact

With this change, when actual usage exceeds the estimate at commit time:

• Previous behavior (REJECT): Commits would fail if the remaining budget couldn't cover the overage
• New behavior (ALLOW_IF_AVAILABLE): Commits will succeed if the remaining budget covers the overage, providing a better user experience while still respecting budget constraints

Users can still explicitly set overage_policy="REJECT" if they prefer the stricter behavior.

https://claude.ai/code/session_01Vzg6nWZUwXaLWEHd2i59mT