Add comprehensive release notes for v0.5.0

[Copilot]

This PR adds comprehensive release notes for the v0.5.0 release, documenting all changes between v0.4.1 and the current main branch.

Overview

The release notes follow the established format from previous releases (v0.4.1, v0.4.0, etc.) and provide a detailed overview of the changes introduced in v0.5.0, primarily from PR #62.

What's Included

The release notes document covers:

• New Features: Introduction of qr_null_pullback! and lq_null_pullback! functions for computing gradients through nullspace decompositions
• API Changes: Renaming of pullback functions (qr_compact_pullback! → qr_pullback!, lq_compact_pullback! → lq_pullback!)
• Internal Improvements: Refactored truncation interface, enhanced ChainRules integration, and code quality improvements
• Migration Guide: Clear examples showing how to update code from v0.4.1 to v0.5.0

Format

The release notes are structured with:

• Clear section headers with emoji markers for easy navigation
• Detailed explanations of user-facing changes
• Code examples in the migration guide
• Links to the full diff and merged pull requests
• Consistent styling with previous releases

The file can be used directly when creating the GitHub release for v0.5.0.

Original prompt

I want to prepare release notes for a v0.5.0 release, which describes the changes between 0.4.1 and the current latest commit

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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[lkdvos]

Not bad!