Node creators in narps_open.core.nodes

[bclenet]

Changes proposed in this Pull Request:

• Adding NodeCreator to easily generate nodes from narps_open.core functions
• 📘 documentation added
• 🔬 tests added

Checklist:

• Descriptive title
• Targets the main branch
• Changes are functional
• My code is explicit and comments were added to it
• Code conforms with PEP8
• Tests were added for the changes and they complete successfully
• Existing tests were updated (if needed) and they complete successfully
• Documentation was updated