multiple return keys for tuple returning functions

[jucordero]

Description

This PR adjusts the behaviour of the pipeline_node decorator to allow functions returning multiple values to store their outputs in multiple keys of the datablock simultaneously

The decorator has two reserved keywords: return_key and return_keys which can only be used to identify the datablock path where results should be stored and cannot be used as part of the function signature.

Checklist

• Follow the Contributor Guidelines
• Write unit tests
• Write documentation strings

[Copilot]

Pull request overview

This PR updates the pipeline_node decorator to support mapping multi-value (tuple) returns into multiple keys in the pipeline datablock, via a new reserved kwarg return_keys (in addition to return_key).

Changes:

• Add return_keys as a reserved kwarg name for pipeline_node-decorated functions.
• Allow passing return_keys to write tuple-return outputs into multiple datablock keys.
• Keep backward-compatibility intent by falling back to return_key when return_keys is not provided.

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[Copilot]

Pull request overview

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

Comments suppressed due to low confidence (1)

agrifoodpy/pipeline/pipeline.py:479

• The reserved-parameter ValueError message is missing spaces due to implicit string concatenation, which makes the exception hard to read (e.g., ".Please rename..." and "thepipeline_node"). Consider formatting it as a single, well-spaced message (optionally factoring out the reserved params set) for clarity.

        if reserved & set(signature(func).parameters):
            raise ValueError(f"Function {func.__name__} has reserved parameter"
                             f" names {reserved & set(signature(func).parameters)}."
                             "Please rename these parameters to use the"
                             "pipeline_node decorator.")