feat: Capture solver log in SolverMetrics

[FBumann]

Summary

• Add solver_log: str | None field to SolverMetrics for programmatic access to solver output after solving
• In Model.solve(), capture the solver log from a temp file (or user-provided log_fn) and attach it to metrics
• Handles edge cases: file creation failure (graceful fallback), encoding (UTF-8 with replace), cleanup (Path.unlink(missing_ok=True))
• Log is captured in finally so it's available even when the solver fails

Blocked by

• feat: add unified SolverMetrics PyPSA/linopy#583 (base branch)

Changes proposed in this Pull Request

• linopy/constants.py: Add solver_log field to SolverMetrics, with truncated display in __repr__
• linopy/model.py: Create temp log file when log_fn is not provided, read log into solver_log on metrics after solving
• test/test_optimization.py: Add test_solver_log_captured and test_solver_log_with_log_fn tests

Checklist

• Code changes are sufficiently documented; i.e. new functions contain docstrings and further explanations may be given in doc.
• Unit tests for new features were added (if applicable).
• A note for the release notes doc/release_notes.rst of the upcoming release is included.
• I consent to the release of this PR's code under the MIT license.

Test plan

• test_solver_log_captured — verifies solver_metrics.solver_log is non-empty after solve (all solver/io_api combos)
• test_solver_log_with_log_fn — verifies log capture when log_fn is explicitly provided
• Verified across all 17 solver/io_api combinations (gurobi, highs, cbc, scip, cplex, xpress, mosek × lp/mps/direct)
• Existing test_solver_metrics.py tests still pass

🤖 Generated with Claude Code

[coderabbitai]

Important

Review skipped

Auto reviews are disabled on base/target branches other than the default branch.

Please check the settings in the CodeRabbit UI or the .coderabbit.yaml file in this repository. To trigger a single review, invoke the @coderabbitai review command.

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: b654d371-5855-4607-8204-94d12103f607

You can disable this status message by setting the reviews.review_status to false in the CodeRabbit configuration file.

Use the checkbox below for a quick retry:

• 🔍 Trigger review

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/solver-log-in-metrics

📝 Coding Plan

• Generate coding plan for human review comments

---

Thanks for using CodeRabbit! It's free for OSS, and your support helps us grow. If you like it, consider giving us a shout-out.

❤️ Share

• X
• Mastodon
• Reddit
• LinkedIn

_{Comment @coderabbitai help to get the list of available commands and usage tips.}