Rename SGrid2DMetadata/SGrid3DMetadata __str__ to describe()

[VeckoTheGecko]

Description

This is more accurate as to what the purpose of the code is, and lines up better with the rest of the codebase.

Checklist

• Closes None
• Tests added
• This PR targets the correct branch (main for normal development, v3-support for v3 support)

AI Disclosure

• This PR contains AI-generated content.
  • I have tested any AI-generated content in my PR.
  • I take responsibility for any AI-generated content in my PR.
  • Describe how you used it (e.g., by pasting your prompt): Small refactoring

[VeckoTheGecko]

I've also updated the functionality to match the rest of the .describe() functions (i.e., write to a buffer, so that it prints it to screen automatically)