feat: Add ARM64 builds and universal installation script

[jbrinkman]

🚀 Implementation of GitHub Issue #45

This PR implements a comprehensive solution for ARM64 platform support and provides a universal installation method for DotNetApiDiff.

✨ Key Features

🏗️ Enhanced Release Pipeline

• ARM64 builds for all platforms: Windows, Linux, and macOS
• Maintains x64 compatibility: Existing builds continue to work
• 6 total release assets: 3 platforms × 2 architectures
• Automated workflow: No manual intervention required

📦 Universal Installation Script (install.sh)

• Cross-platform compatibility: Works on all Linux distributions and macOS
• Automatic platform detection: Detects OS and CPU architecture
• Smart fallback logic: Tries ARM64 first, falls back to x64 if unavailable
• Security-first approach: SHA256 checksum verification
• Flexible installation options:
  • User installation (~/.local/bin) - default
  • System installation (/usr/local/bin) - with --system flag
  • Custom directory - with --prefix option
• PATH management: Automatically updates shell configuration
• Version control: Install latest or specific versions

📚 Updated Documentation

• Quick install commands for immediate use
• Platform-specific download links for manual installation
• ARM64 support clearly documented
• Multiple installation methods covered

🎯 Usage Examples

# Quick install (latest version)
curl -fsSL https://raw.githubusercontent.com/jbrinkman/dotnet-api-diff/main/install.sh | bash

# Install specific version
curl -fsSL https://raw.githubusercontent.com/jbrinkman/dotnet-api-diff/main/install.sh | bash -s -- v1.2.3

# System-wide installation (requires sudo)
curl -fsSL https://raw.githubusercontent.com/jbrinkman/dotnet-api-diff/main/install.sh | sudo bash -s -- --system

# Custom installation directory
curl -fsSL https://raw.githubusercontent.com/jbrinkman/dotnet-api-diff/main/install.sh | bash -s -- --prefix /opt/mytools

🔧 Technical Details

Release Assets (New Naming Convention)

• dotnet-api-diff-win-x64.zip / dotnet-api-diff-win-arm64.zip
• dotnet-api-diff-linux-x64.tar.gz / dotnet-api-diff-linux-arm64.tar.gz
• dotnet-api-diff-osx-x64.tar.gz / dotnet-api-diff-osx-arm64.tar.gz

Installation Script Features

• Error handling: Comprehensive error messages and graceful failures
• Dependency checking: Validates required tools (curl, tar, etc.)
• Checksum verification: Downloads and verifies SHA256 hashes
• Clean installation: Removes temporary files automatically
• Version validation: Ensures requested versions exist
• Force overwrite: Option to replace existing installations

🧪 Testing

• ✅ ARM64 build compatibility tested with .NET 8.0
• ✅ Installation script tested on macOS ARM64 with fallback to x64
• ✅ Binary functionality verified with --version command
• ✅ Checksum verification working correctly
• ✅ Cross-platform archive formats (tar.gz for Unix, zip for Windows)

🎁 Benefits

1. Native ARM64 performance on Apple Silicon Macs and ARM64 Linux servers
2. Simplified installation - single command for any platform
3. Enhanced security with checksum verification
4. Backward compatibility - existing installations continue to work
5. Future-ready - automatically supports new ARM64 builds when available

📋 Files Changed

• .github/workflows/release.yml - Added ARM64 builds to release pipeline
• install.sh - New universal installation script
• README.md - Updated installation documentation

🔄 Deployment Impact

• Next release will automatically include all 6 platform/architecture combinations
• Install script gracefully handles both new and legacy releases
• Zero breaking changes to existing workflows or installations

🎯 Closes

Fixes #45 - Create universal installation script for Linux and macOS

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This implementation provides a complete solution for ARM64 support while maintaining excellent backward compatibility and user experience. The universal installer makes DotNetApiDiff accessible to users who prefer not to use package managers or need specific versions not yet available in package repositories.