Add ensure_ transition methods for safe state transitions

[stimms]

Summary

• Adds ensure_#{transition_name} and ensure_#{transition_name}! methods that gracefully handle the case when a record is already in the target state
• Returns true instead of raising an error when already in the destination state
• The bang variant still raises on invalid transitions; the non-bang variant returns false

Test plan

• Added tests verifying ensure_ methods return true when already in target state
• Added tests verifying ensure_ methods perform normal transitions when not in target state
• Added tests verifying ensure_! raises on invalid transitions
• Added tests verifying ensure_ without bang can skip save
• All existing tests continue to pass

🤖 Generated with Claude Code

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Note

Medium Risk
Adds new generated transition methods that change how callers can invoke state changes (idempotent when already in target state). Risk is moderate because it affects the core transition method generator and could alter application control flow around persistence/validation expectations.

Overview
Adds generated ensure_<transition> and ensure_<transition>! methods for every stator transition, which return true without performing validation/saving when the record is already in the transition’s target state; otherwise they delegate to the existing transition methods (including should_save behavior for the non-bang version).

Extends model specs to cover idempotent behavior, normal delegation when not in the target state, true return values, optional skip-save semantics, and bang-method failure on invalid transitions.

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