Allow PlotGenerator init without suggestions; make Groq dependency optional

[tosincarik]

Summary

This PR fixes a mismatch between type hints and runtime behavior in PlotGenerator, and improves install/import ergonomics by making the groq dependency optional.

Changes

PlotGenerator

• Allow initializing PlotGenerator(..., suggestions=None) (matches Optional[pd.DataFrame] signature).
• Raise a clear ValueError when generate_plot() is called without suggestions.
• Add a regression test covering the new behavior.

Optional Groq dependency

• Guard Groq imports with try/except ImportError so import plotsense works without groq installed.
• Skip Groq key validation when the Groq client isn’t available.
• Update tests to handle the optional-dependency behavior.

Notes

• This PR contains two commits:
  • Allow PlotGenerator initialization without suggestions
  • Make Groq dependency optional in tests

[christianchimezie]

Hi @tosincarik, apologies for just getting back to this. The active branch is the developer branch, hence it is the developer branch that should be cloned or forked and merged back into.