Enhance pyautoplot with new plot types, reports, and data cleanup

- Added Correlation Heatmap and Violin Plots.
- Implemented `cleanup()` method for handling missing values.
- Improved automatic date detection for string columns.
- Added `export_json()` for statistical analysis data.
- Added `export_report()` for comprehensive HTML and PDF reports.
- Optimized performance and memory usage.
- Updated `test.py` with comprehensive examples.

Co-authored-by: Infinitode <107624055+Infinitode@users.noreply.github.com>

Author: google-labs-jules[bot]