Added missing imports for builtin nodes

[b3by]

Description

This PR adds missing imports for a number of built-in nodes that were not included in the node namespace.

PR type
Select all the labels that apply to this PR.

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Code refactoring
• Performance improvement
• Test update
• Build/CI configuration change
• Other (please describe):

Key modifications and changes

The missing nodes are now added to the juturna.nodes namespace.