Add CORrelation ALignment domain adaptation

[shuo-zhou]

Description

Add CORAL (CORrelation ALignment) domain adaptation

Status

Work in progress

Types of changes

• Non-breaking change (fix or new feature that would not break existing functionality).
• Breaking change (fix or new feature that would cause existing functionality to change).
• New tests added to cover the changes.
• In-line docstrings updated and documentation docs updated.

[codecov]

Codecov Report

❌ Patch coverage is 96.25000% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.40%. Comparing base (5b9ef29) to head (9cfb315).

Files with missing lines	Patch %	Lines
kalelinear/transformer/_coral.py	96.10%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #21      +/-   ##
==========================================
+ Coverage   90.16%   90.40%   +0.23%     
==========================================
  Files          24       25       +1     
  Lines        1922     2000      +78     
==========================================
+ Hits         1733     1808      +75     
- Misses        189      192       +3     

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[Copilot]

🟡 Changes recommended

The whitening cutoff can collapse valid low-scale covariance matrices to a zero alignment.

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Pull request overview

Adds CORAL domain adaptation with public exports, documentation, and tests.

Changes:

• Implements covariance-based source-to-target alignment.
• Exposes CORAL through transformer and embedding APIs.
• Adds validation, numerical, API, and documentation coverage.

File summaries

File	Description
kalelinear/transformer/_coral.py	Implements CORAL.
kalelinear/transformer/__init__.py	Exports CORAL.
kalelinear/embed.py	Adds embedding API alias.
tests/transformer/test_coral.py	Tests CORAL behavior and validation.
tests/test_public_api.py	Verifies public exposure.
README.md	Documents feature and citation.
TUTORIALS.md	Adds usage example.
docs/source/usage.rst	Describes domain alignment behavior.
docs/source/tutorial.rst	Adds CORAL tutorial.
docs/source/introduction.rst	Lists CORAL among transformers.
docs/source/api_transformers.rst	Adds generated API documentation.

Review details

• Files reviewed: 11/11 changed files
• Comments generated: 1
• Review effort level: Balanced

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