Attribute Macro update_validator 

#[update_validator]

Marks a method within a #[workflow_methods] impl block as a validator for an update handler. This attribute is processed by the #[workflow_methods] macro and should not be used standalone.

The parameter specifies which update this validator applies to: #[update_validator(my_update)]

The validator method must:

• Take &self (not &mut self)
• Take &WorkflowContextView as the first parameter
• Take a reference to the update’s input type as the second parameter
• Return Result<(), Box<dyn std::error::Error + Send + Sync>>