Summary

Removes the step_duration parameter from Model.__init__(). Since this was added in #2903 but not yet released, it can be removed without deprecation.

Motive

The step_duration parameter conflicts with Mesa's direction of making model.time the universal source of truth and eventually deprecating steps. Having configurable step duration confuses the mental model (users must understand how discrete steps map to continuous time), complicates future migration (we'd need to explain what happens to step_duration when steps is deprecated), and serves limited real-world use cases (non-unit step durations are rarely needed and can be handled via discrete event simulators). Removing it now gives us simple, predictable behavior (each step() advances time by 1.0) and a clean path to eventually deprecate steps in favor of model.time.

If our vision what that model.steps is a core feature, it made sense. But the direction is to move to time, so a new steps feature doesn't make much sense.

I also violated the principle of atomic PRs by adding it in #2903. It should have been a separate discussion, PR and review process. Sorry.

Implementation

Remove from Model.__init__():

• step_duration: float = 1.0 parameter
• self._step_duration: float = step_duration attribute
• Update _wrapped_step() to use self.time += 1.0 instead of self.time += self._step_duration
• Remove step_duration from docstring

Additional Notes

• Aligns with vision in The time variable in mesa.Model #2228 and Proposal: Unified Time and Event Scheduling API #2921
• No migration guide needed (unreleased feature)
• Advanced users can still control time via discrete event simulators