make output_dir configurable in evals

[mikasenghaas]

Adds an output_dir field to EvalConfig that overrides the default ./outputs fallback in path resolution. Can be set via output_dir in eval TOML configs.

Description

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Test improvement

Testing

• All existing tests pass when running uv run pytest locally.
• New tests have been added to cover the changes

Checklist

• My code follows the style guidelines of this project as outlined in AGENTS.md
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published

Additional Notes

---

Note

Low Risk
Low risk: adds an optional output_dir override to evaluation path resolution without changing default behavior when unset. Main risk is misconfiguration leading to results/resume lookup writing to or scanning an unexpected directory.

Overview
Adds a new optional output_dir field to EvalConfig and allows it to be set from eval TOML/CLI configs.

Updates output path resolution in path_utils so eval/GEPA results (and --resume auto-detection via find_latest_incomplete_eval_results_path) use output_dir when provided, otherwise preserving the existing environment-local outputs/ or ./outputs fallback behavior.

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