Update Changelog.md

[Copilot]

• Review the keepachangelog.com format and understand the style requirements
• Analyze the MatrixAlgebraKit decompositions PR MatrixAlgebraKit decompositions #230 commit message for changes
• Update Changelog.md with a new v0.15 section following keepachangelog style
• Include brief descriptions of changes with references to PR MatrixAlgebraKit decompositions #230
• Keep descriptions concise and direct to relevant PRs/commits

Original prompt

I would like to make sure that the Changelog.md file is updated to reflect the latest series of changes, which includes everything that comes later in time than the v0.14 release. The style of the changelog should be similar to what can be found at https://keepachangelog.com/en/1.1.0/. Try not to overexagerate and keep it brief, preferring to direct to the relevant PRs and commits for further clarification.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
see 46 files with indirect coverage changes

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