deps: restore pytest-codeblocks for docs

[kmarchais]

Summary

• restore pytest-codeblocks for documentation code-block testing
• require pytest-codeblocks 0.18.0 now that it supports newer pytest releases
• remove the custom pytest-examples docs test and use pytest --codeblocks docs/ again
• update docs skip markers to pytest.mark.skip where snippets should not execute

Validation

• uv lock --check
• uv run python -c "import pytest, importlib.metadata as m; print('pytest', pytest.version); print('pytest-codeblocks', m.version('pytest-codeblocks'))"
• uv run pytest --codeblocks docs/ --collect-only -q
• uv run pytest --codeblocks docs/ -q
• uv run pytest --ignore=tests/examples_test.py -q

[github-actions]

📖 Docs preview: https://kmarchais.github.io/mmgpy/pr-336/

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.18%. Comparing base (3980e09) to head (0c7cb0d).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #336   +/-   ##
=======================================
  Coverage   86.18%   86.18%           
=======================================
  Files          29       29           
  Lines        3865     3865           
  Branches      684      684           
=======================================
  Hits         3331     3331           
  Misses        330      330           
  Partials      204      204           

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[github-actions]

Benchmark Results Summary

Group	Benchmarks	Mean Time Range
duplicate-detection	2	5.85ms - 70.16ms
operations	6	0.14ms - 55.28ms
remesh-2d	3	187.58ms - 189.21ms
remesh-3d	3	2717.71ms - 9739.93ms
remesh-surface	4	192.04ms - 476.66ms

Total: 18 benchmarks

---

Benchmark Comparison Results

Status: ✅ PASS
Compared: 18 benchmarks (threshold: 1.3x)

18 benchmarks passed

Benchmark	Baseline	Current	Ratio
test_metric_field_set_get	109.2us	140.1us	1.28x
test_3d_optimize	2.39s	2.72s	1.13x
test_quality_3d	296.3us	317.1us	1.07x
test_pyvista_roundtrip_3d	32.66ms	34.62ms	1.06x
test_3d_adaptive_hmin_hmax_hausd	7.77s	8.10s	1.04x
test_validate_3d	13.37ms	13.66ms	1.02x
test_io_roundtrip_3d	54.59ms	55.28ms	1.01x
test_2d_adaptive_hmax_hgrad_angle	187.10ms	189.21ms	1.01x
test_surface_uniform	347.95ms	350.74ms	1.01x
test_surface_metric_hmax_hausd_angle	474.19ms	476.66ms	1.01x
test_2d_uniform_angle	187.14ms	187.78ms	1.00x
test_duplicate_detection_10k	5.83ms	5.85ms	1.00x
test_duplicate_detection_100k	70.05ms	70.16ms	1.00x
test_2d_metric_hmin_hausd	187.29ms	187.58ms	1.00x
test_3d_metric_hgrad	9.73s	9.74s	1.00x
test_construction_3d	28.96ms	28.95ms	1.00x
test_surface_optimize	473.16ms	472.02ms	1.00x
test_surface_adaptive_hmin_hgrad	202.40ms	192.04ms	0.95x