add 3DRP but also remove optional fields

[CPernet]

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📚 Documentation preview 📚: https://pet2bids--363.org.readthedocs.build/en/363/

[Copilot]

Pull Request Overview

This pull request adds support for the 3DRP (3D Kinahan-Rogers) reconstruction method while simplifying the metadata structure by removing optional fields when they are not applicable. The changes improve the flexibility of reconstruction method handling by making parameter fields conditional based on whether actual parameters exist.

Key changes:

• Adds 3DRP reconstruction method to PET metadata definitions
• Makes ReconMethodParameterUnits and ReconMethodParameterValues conditional fields rather than mandatory
• Implements dynamic field removal when reconstruction parameters are set to "none"

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
metadata/PET_reconstruction_methods.json	Adds 3DRP method definition and removes null parameter fields from existing methods
metadata/PET_metadata.json	Moves parameter fields from mandatory to optional and adds ReconFilterSize to recommended
matlab/updatejsonpetfile.m	Implements conditional field handling and removes fields when set to "none"

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[CPernet]

the validator does not accept some changes - to be re-checked