workflows4: Fix workflow scripts and enhance prun options validation

[mightqxc]

No description provided.

[Copilot]

Pull request overview

This PR extends the native workflow tooling by adding an on-worker merge script, making the multistep_merge workflow template more self-contained (defaults + sandboxing the merge script), and expanding the workflow description schema to support secondary datasets, file-type filters, and containers.

Changes:

• Add and package share/workflow_scripts/merge.sh and update the multistep_merge template to use it (including copying it into the sandbox).
• Extend WorkflowDescription/WorkflowStep to serialize/validate new step attributes: inDsType, secondaryDSs, secondaryDsTypes, containerImage, and useAthenaPackages.
• Adjust pchain_native startup to restore Rucio-related import paths from the original PYTHONPATH.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
share/workflow_scripts/merge.sh	New worker-node merge helper that consumes --writeInputToTxt output and runs hadd.
setup.py	Installs the new workflow script into etc/panda/share/workflow_scripts.
pandaclient/workflow_templates/multistep_merge.py	Adds defaults, script discovery/copy-to-sandbox behavior, and configurable output/input filenames.
pandaclient/workflow_description.py	Expands step schema + validation and updates documentation examples.
pandaclient/PChainScript_native.py	Restores selected paths from the original environment to support importing rucio.
packages/full/pyproject.toml	Ensures workflow scripts are included as shared wheel data.
examples/signal_background_combine_wfd.yaml	Adds a multi-branch workflow example using secondary datasets and type filters.

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