docs: improve documentation with LaTeX math and benchmark results

[ChanceSiyuan]

Summary

• Add MathJax support via pymdownx.arithmatex extension for proper LaTeX rendering
• Create mathjax.js config for proper math rendering
• Convert mathematical_description.md to use proper LaTeX notation
• Add benchmark results section to getting_started.md
• Include threshold plots and decoder comparison images

Changes

LaTeX Support

• Updated mkdocs.yml with pymdownx.arithmatex extension
• Created docs/javascripts/mathjax.js for MathJax configuration
• Converted docs/mathematical_description.md to use proper LaTeX:
  • Message passing formulas: $\mu_{f \to x}(x)$
  • Damping update formula
  • Convergence conditions
  • Marginal probability computation

Benchmark Results

• Added benchmark images to docs/images/:
  • threshold_plot.png
  • threshold_comparison.png
  • bp_failure_demo.png
  • osd_success_demo.png
• Added Benchmark Results section to docs/getting_started.md with:
  • Threshold comparison plots
  • BP vs BP+OSD comparison
  • Decoding examples
  • Performance summary table

Closes #69

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.18%. Comparing base (7d3d79f) to head (59d7c63).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #72   +/-   ##
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  Coverage   95.18%   95.18%           
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  Files          10       10           
  Lines         747      747           
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  Hits          711      711           
  Misses         36       36           

Flag	Coverage Δ
unittests	95.18% <ø> (ø)

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