1.4.0 release

[mmschlk]

Motivation and Context

Makes the 1.4.0 release.

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Public API Changes

• No Public API changes
• Yes, Public API changes (Details below)

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How Has This Been Tested?

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Checklist

• The changes have been tested locally.
• Documentation has been updated (if the public API or usage changes).
• An entry has been added to CHANGELOG.md (if relevant for users).
• The code follows the project's style guidelines.
• I have considered the impact of these changes on the public API.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[Copilot]

Pull Request Overview

This PR prepares the v1.4.0 release with multiple improvements including documentation updates, removal of unused imports, and improved CI testing matrix. Key changes include:

• Improved docstrings for GaussianImputer and GaussianCopulaImputer classes with better formatting and clarity
• Removed unused typing_extensions imports and @override decorators from imputer classes
• Enhanced CI workflow to test across multiple Python versions (3.10, 3.12, 3.13) and operating systems (Ubuntu, Windows, macOS)
• Updated project metadata to add a new maintainer and author

Reviewed Changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 3 comments.

Show a summary per file

File	Description
src/shapiq/imputer/gaussian_imputer.py	Removed unused typing_extensions import and @override decorator; improved docstring formatting with better parameter descriptions
src/shapiq/imputer/gaussian_copula_imputer.py	Removed unused typing_extensions import and @override decorator; added comprehensive docstring for __init__ method
pyproject.toml	Added Santo M. A. R. Thies as author and maintainer
README.md	Reorganized ProxySPEX section to appear before visualizations section for better flow
CHANGELOG.md	Restructured and finalized v1.4.0 release notes with detailed sections for features, breaking changes, bugfixes, and maintenance
.github/workflows/ci.yml	Expanded CI testing matrix to include Python 3.10, 3.12, 3.13 across Ubuntu, Windows, and macOS; removed emoji from success messages

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