Bump to v1.3.1 and refresh benchmark artifacts

[daggbt]

Summary

Bump the project metadata to 1.3.1 and refresh the checked-in benchmark artifacts that back the docs and release notes.

What changed

• update project version metadata in pyproject.toml and uv.lock
• add the 1.3.1 release entry in the changelog
• refresh benchmark result JSON, text output, and plots under benchmarks/results
• sync the mirrored benchmark assets under docs/assets/benchmarks

Validation

• local commit hooks passed during commit: ruff, ruff format, pyright, and pytest