Update autotuning documentation to reflect current interface

[ChrisRackauckas-Claude]

Summary

This PR updates the LinearSolveAutotune documentation to accurately reflect the current implementation, including the simplified AutotuneResults-based interface and GitHub-based result sharing workflow.

Changes

Interface Updates

• Updated to reflect that autotune_setup() returns an AutotuneResults object containing results_df and sysinfo
• Documented the plot(results) method for generating performance visualizations
• Documented the share_results(results) function for community sharing
• Removed outdated references to the old three-value return signature

Content Improvements

• Clarified size categories: Documented all five categories (:tiny, :small, :medium, :large, :big) with their actual size ranges
• Updated defaults: Correctly documented that Float64 is the default element type and [:tiny, :small, :medium, :large] are the default sizes
• GitHub authentication: Added comprehensive instructions for both gh CLI and personal access token methods
• Privacy information: Added clear notes about optional sharing and what data is collected
• Advanced usage: Added sections on custom pipelines and batch testing
• Troubleshooting: Added common issues and solutions

Examples Added

• Performance data analysis with DataFrames
• Plotting and saving visualizations
• Accessing system information from results
• Custom benchmark pipelines
• Batch testing multiple configurations
• GPU-specific configurations

Documentation Structure

The updated documentation follows a logical progression:

1. Quick Start - Get users running immediately
2. Understanding Results - Explain what they're looking at
3. Customization - Show how to tailor benchmarks
4. Sharing - Community contribution workflow
5. Working with Results - Data analysis and visualization
6. Advanced Usage - Power user features
7. Troubleshooting - Common problems and solutions

Related Issues

• Implements documentation for the current autotuning system
• References community benchmark collection issue Autotune Results #669

🤖 Generated with Claude Code

Co-Authored-By: Claude [email protected]