add size sorting task

[jyizheng]

This pull request introduces a new "Size Sorting Task" for visual reasoning, where scattered bars must be sorted by height. The implementation includes a new generator, configuration, and CLI entry point for dataset generation, as well as updates to the documentation and module exports.

New Task: Size Sorting (Bar Height Sorting)

• Adds a visual reasoning task where the goal is to sort randomly scattered bars by height and align them at the baseline. This includes prompt templates, configuration, rendering logic, and optional animation video generation.

Command-Line Interface & Entry Point

• Introduces examples/generate_size_sorting.py, a CLI tool for generating datasets for the size sorting task with customizable parameters (number of bars, sort order, etc.).

Documentation

• Updates README.md to document the new size sorting task, including its description, usage examples, configuration options, and output structure.

Module Exports

• Updates src/__init__.py to export the new size sorting task classes and prompt function, making them available for import elsewhere in the codebase.