docs: Add examples for all methods

[Marius Merkle (MariusMerkleQC)]

Motivation

Solves #22. Claude examples for all methods in DataFrameComparison, Schemas, and the assert_{frame,colection}_equal methods (I verified them). Please give it a look here. For instance, the change_counts() method now looks as follows:

Changes

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (cccfad4) to head (9b23fef).

Additional details and impacted files

@@            Coverage Diff            @@
##              main       #24   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           10        10           
  Lines          758       758           
=========================================
  Hits           758       758           

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[Copilot]

Pull request overview

Adds doctest-style usage examples across the public API so users can more easily understand diffly’s comparison and testing helpers, addressing the documentation gap described in #22.

Changes:

• Added usage examples to compare_frames() and many DataFrameComparison/Schemas methods.
• Added usage examples to assert_frame_equal() and assert_collection_equal().

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
diffly/testing.py	Adds docstring examples for the testing assertions.
diffly/comparison.py	Adds docstring examples for compare_frames, DataFrameComparison methods, and Schemas APIs.

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