Misleading Section Heading in Internal API

[philipc2]

Under the Internal API, the heading "Grid Parsing and Encoding" contains groups of functions that don't belong to that family, specifically:

• Core Utils
• Visualization
• Slicing
• Subsetting
• Neighbor
• Gradients

https://uxarray.readthedocs.io/en/latest/internal_api/index.html#grid-parsing-and-encoding

These should be under a general "Helper" section, including their previous sub-heading.

Something like what we have in our user API

https://uxarray.readthedocs.io/en/latest/user_api/index.html#helpers

Would be good to look through and see if any other sections could use modifications also.