feat(python): Improve Jupyter notebook support with SQL magic commands and examples

[littleKitchen]

Summary

This PR implements the improvements outlined in #1398 to enhance the Jupyter notebook experience for Ballista.

Implementation Checklist

All items from the issue have been implemented:

• ✅ Add example .ipynb notebooks to python/examples/

  • getting_started.ipynb - Basic connection and queries
  • dataframe_api.ipynb - DataFrame transformations
  • distributed_queries.ipynb - Multi-stage query examples

• ✅ Document notebook support in Python README

  • Added comprehensive Jupyter section with examples for magic commands, HTML rendering, and plan visualization

• ✅ Create ballista.jupyter module with magic commands

  • Full implementation with BallistaMagics class
  • Graceful fallback when IPython is not available

• ✅ Add %ballista connect/status/tables/schema line magics

  • connect: Connect to Ballista cluster
  • status: Show connection status
  • tables: List registered tables
  • schema: Show table schema
  • disconnect: Disconnect from cluster
  • history: Show query history

• ✅ Add %%sql cell magic

  • Line magic for single-line queries (%sql SELECT ...)
  • Cell magic for multi-line queries (%%sql)
  • Variable assignment support (%%sql my_result)
  • --no-display and --limit N options

• ✅ Add explain_visual() method for query plan rendering

  • Generates DOT/SVG visualization of execution plans
  • Supports Jupyter _repr_html_ for inline display
  • Fallback HTML representation when graphviz is not installed
  • .save() method for exporting to files

• ✅ Add progress indicator support for long-running queries

  • collect_with_progress() method on DataFrame
  • Callback support for custom progress handling
  • Jupyter-aware progress display

• ✅ Consider JupySQL integration

  • Documented as alternative in README for users who prefer the JupySQL ecosystem

Additional Improvements

• ExecutionPlanVisualization class for plan rendering with DOT/SVG conversion
• tables() method on BallistaSessionContext for listing registered tables
• Optional jupyter dependency group in pyproject.toml
• Comprehensive test coverage with 45 tests passing

Usage Examples

# Load the extension
%load_ext ballista.jupyter

# Connect to a Ballista cluster
%ballista connect df://localhost:50050

# Execute SQL queries
%sql SELECT COUNT(*) FROM orders

%%sql my_result
SELECT customer_id, SUM(amount) as total
FROM orders
GROUP BY customer_id
ORDER BY total DESC
LIMIT 10

# Visualize execution plan
df.explain_visual()

# Track progress on long queries
batches = df.collect_with_progress()

Testing

All 45 tests pass:

• Existing tests: 6 passed
• New Jupyter module tests: 20 passed
• New notebook features tests: 19 passed

Closes #1398