Add reset() to trace.model

[allenanie]

Multiple people asked me if there's a simple way to reset parameter node value back to original. Will work on adding this.

[allenanie]

But to support LangGraph, we might need a more general reset() on the parameter level, not just on the @model level.

[chinganc]

Do you mean to reset it to the first value that the parameter is initialized to? or setting it to some user-given value?

[allenanie]

Initial value (This request was asked by Xavier and some other people)

[chinganc]

We can create a new attribute/property for a node, e.g., init_data, which supports read and write.