Update documentation

[MatthewFilipovich]

Update 4f examples with smaller shape, and other minor changes.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 99.92%. Comparing base (f2472b1) to head (974c4c8).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

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  Coverage   99.92%   99.92%           
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  Files          38       38           
  Lines        1305     1305           
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  Hits         1304     1304           
  Misses          1        1           

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[Copilot]

Pull request overview

Updates documentation and example scripts to use smaller default grid sizes for faster execution/rendering, while clarifying a few theoretical descriptions (LG mode notation, Gaussian Schell-model normalization, and inner-product definition).

Changes:

• Reduce grid shape and adjust related physical parameters (focal length, tile length, filter radius, propagation distances) in README, quickstart, and the 4f example.
• Clarify documentation math/notation: Laguerre–Gaussian mode superscript sign, normalized Gaussian intensity for the Gaussian Schell-model, and explicit Field.inner convention in the user guide.

Reviewed changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
README.md	Shrinks the 4f example parameters to a smaller grid and consistent physical scales.
examples/optimization/training_petal_beam.py	Clarifies LG mode notation in the narrative comment.
examples/optical_systems/4f_system.py	Uses smaller grid/physical parameters; updates plane count wording to match the 0…4f planes.
docs/source/user-guide/spatial_coherence.rst	Documents the normalized Gaussian intensity used by gaussian_schell_model.
docs/source/user-guide/propagation.rst	Refines the description of the critical-distance geometry term.
docs/source/user-guide/fields.rst	Aligns the inner-product equation/notation with the library’s Field.inner convention.
docs/source/quickstart/index.rst	Updates quickstart plots/examples to smaller grids and adjusted distances/parameters.

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