docs: add documentation for pre updator effects

[Pierre-MarieMarchio]

Description:

Update the documentation to explain how to use pre-effects:

• Implement effects that execute before updators (pre-effects)
• Configure different execution timings of effects in the flow
• Maintain type safety when using pre-effects

This documentation will guide users on how to use these features and understand their scope and lifecycle.

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Tasks:

• Document the concept of pre-effects

  • Explain what pre-effects are and why they're useful
  • Provide an example of registering pre-effects (with code)
  • Explain how pre-effects integrate into the existing unidirectional flow

• Document pre-effect use cases

  • Explain scenarios where pre-effects are preferable to standard effects
  • Provide examples of payload validation and payload generation
  • Mention limitations and specific use cases (such as testing or isolated behaviors)

• Lifecycle and execution order

  • Describe the new execution order with pre-effects: Action → Pre-Effect → Updator → Effect
  • Explain how to configure effect timing ({ timing: 'pre' | 'post' })
  • Detail how pre-effects can modify or generate payloads before updators

• Type safety

  • Explain type constraints for pre-effects and their returns
  • Document how to maintain type consistency between actions and pre-effects
  • Provide code examples illustrating type safety in different scenarios

• Action cancellation

  • Document how pre-effects can be used to cancel actions
  • Provide examples of validation that prevents updator execution

• Provide complete code snippets

  • Add working examples for pre-effects with and without payload
  • Ensure examples are clear and demonstrate real-world usage scenarios

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Expected Outcome:

• The documentation should provide a clear, structured explanation of pre-effect usage.
• Code snippets should be easy to understand and relevant to typical use cases.
• Developers should be able to easily integrate these patterns into their own projects.