hist(group): add validation & empty-data handling; docstring, guide and tests

[Subat-01]

Background

Table.hist needed clearer documentation and safer behavior for the group argument.

Changes

Code

• datascience/tables.py:hist
  • Validate group is a legal column (label or index); otherwise raise ValueError with a clear message.
  • Keep existing constraints: group cannot be used with bin_column; and grouping allows only one numeric data column.
  • When the grouped subset is empty, return an empty figure safely (avoid exceptions).
  • Expanded docstring with two examples:
    • t.hist('height', group='gender')
    • t.hist('height', group='gender', side_by_side=True)

Docs

• New docs/hist_grouping.md:
  • Minimal example and explanation of constraints + empty-data behavior.
  • (If the project prefers RST/toctree only, I'm happy to convert to .rst and add it to the TOC.)

Tests

• tests/test_hist_group.py
  • Valid grouping runs without error.
  • Non-existent group column raises ValueError.
  • Empty grouped subset renders safely (creates an empty plot).

(Optional) Maps small fixes

• datascience/maps.py
  • Provide default attribution when a string tile style is used and no attr supplied (Folium >= 0.20).
  • Mirror text_color -> textColor option for BeautifyIcon for backward compatibility.

Verification

• Local run: 225 passed, 1 skipped, 0 failed.

Files changed (for quick review)

• datascience/tables.py [around lines ~5310, ~5398, ~5420, ~5455]
• docs/hist_grouping.md
• tests/test_hist_group.py
• (optional) datascience/maps.py

Compatibility & Notes

• No breaking API changes; clearer errors, docs, and tests.
• Open to adjusting error types/doc placement or dropping the maps tweak if maintainers prefer a focused PR.