Feature Request: Define reusable methods/functions within a single workflow (shared across activities)

Hi 👋,

I'm working with Elsa Workflows and have a question regarding code reuse within a single workflow definition.

**Use case:**
In one workflow, I have multiple Script or Expression Activities that need to use the same helper logic — for example, a `greet(name)` function. Currently, I have to duplicate this function in every activity that needs it.

**My question / feature request:**
Is there a way (or could there be a future feature) to define a shared/global method within a single workflow that all activities in that workflow can reference?

**For example:**

A global method block in the workflow JSON definition

A shared "function library" scoped to the workflow execution

A better way to inject helper logic into all script/expression nodes in a workflow

**Why this matters:**
It would help make workflows more maintainable and DRY, especially when using Script or Expression Activities that rely on repeated logic.

Thanks for considering this! I appreciate all the great work on Elsa 🙌