0.12.0: disable notebook execution in docs CI

[MIWdlB]

Summary

• Bumps version 0.11.0 → 0.12.0 in Cargo.toml, crates/ferrmion-core/Cargo.toml, pyproject.toml, and docs/source/conf.py
• Promotes the [Unreleased] CHANGELOG section to [0.12.0] - 2026-07-27
• Sets nb_execution_mode = "off" in docs/source/conf.py — stops myst_nb from re-executing notebooks during the ReadTheDocs build, fixing the timeout-induced CI failures

Test plan

• ReadTheDocs build succeeds (notebooks are rendered from saved outputs, not re-executed)
• uv run pre-commit run --all passes (verified locally)
• cargo test --workspace passes
• uv run pytest passes

🤖 Generated with Claude Code

[codspeed-hq]

Merging this PR will degrade performance by 3.42%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

❌ 2 regressed benchmarks
✅ 54 untouched benchmarks
⏩ 100 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	test_benchmark_decode_zbasis_ensemble[32-JKMN]	51.4 ms	53.4 ms	-3.74%
❌	Simulation	test_benchmark_decode_zbasis_ensemble[32-BravyiKitaev]	51.4 ms	53 ms	-3.1%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

---

_{Comparing bump-version-0.12.0 (2cec68c) with main (79c2cf0)}

Footnotes

1. 100 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩