feat: create sampling preset for python code generation

[akihikokuroda]

Pull Request

Issue

Fix: #1123

Description

This PR implements issue #1123 by creating reusable sampling presets that combine Mellea requirements with optimized feedback strategies for Python code generation tasks.

What's included

New feedback strategy system (mellea/stdlib/sampling/feedback.py):

• PythonCodeFeedbackStrategy — converts validation failures (syntax errors, import restrictions, output size limits) into targeted repair instructions the model can act on
• Structured feedback messages that include the error, its context, and concrete next steps
• Integration with the existing interactive validation repair loop

Sampling presets (mellea/stdlib/sampling/presets.py):

• python_code_generation_preset() — factory for general Python code generation (syntax validation, execution safety, size constraints)
• python_plotting_preset() — specialized factory for matplotlib/visualization code (adds plotting-specific requirements like figure closure and size limits)
• Both combine requirements + feedback strategy into a ready-to-use Sampling object

Examples:

• docs/examples/sampling/python_code_generation_preset.py — demonstrates the general preset and feedback flow
• docs/examples/sampling/python_plotting_preset.py — shows specialized plotting preset with repair strategies

Tests (test/stdlib/sampling/test_presets.py):

• Feedback generation for each error type
• Preset factory configuration
• Integration with the validation repair loop

Testing

• Tests added to the respective file if code was changed
• New code has 100% coverage if code was added
• Ensure existing tests and github automation passes (a maintainer will kick off the github automation when the rest of the PR is populated)

Attribution

• AI coding assistants used

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Adding a new component, requirement, sampling strategy, or tool?

If your PR adds or modifies one of the types below, check the matching box. A checklist of type-specific review items will be posted as a comment.

• Component
• Requirement
• Sampling Strategy
• Tool

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