Add inline handler support to workflow context

This change introduces a new ctx.run() method that allows executing inline handlers within workflow mutation transactions. The handler receives the mutation context and can perform database operations, with results being journaled for replay consistency.

Key Changes

• Added ctx.run() method to WorkflowCtx that executes inline handlers with access to the mutation context
• Introduced optional internalMutation parameter to workflow definitions for fully typed database access
• Added generic DataModel type parameter to WorkflowDefinition and WorkflowCtx for type safety
• Extended step execution to handle inline handlers alongside existing function calls
• Updated journal processing to support inline-completed steps
• Added comprehensive test coverage for inline handler execution, replay, and error handling

The inline handlers are journaled like other workflow steps, ensuring deterministic replay behavior while providing direct access to the underlying mutation transaction.