Set up comprehensive GitHub Actions CI workflow

[Copilot]

Implements a complete CI/CD solution for FDWaveformView following best practices from swift6-module-template and Alamofire projects, addressing issue #160.

What's Changed

CI Infrastructure

• GitHub Actions workflow with comprehensive testing across multiple Swift versions and platforms
• Swift Package Manager builds on macOS 14 & 15 with Xcode 15.4 & 16.1
• iOS compatibility validation through Example app builds on iOS 17.5 & 18.1
• Automated testing on every pull request and main branch push

Platform Support Updates

• Updated Package.swift to specify minimum platform requirements:
  • iOS 13.0+
  • macOS 10.15+
  • tvOS 13.0+
  • watchOS 6.0+
• Modernized platform targets from the previous iOS 12+ requirement

Testing Enhancements

• Enhanced test suite with basic functionality validation
• Ensured tests verify module import and basic operations
• Tests run automatically in CI environment

Documentation Updates

• Updated CONTRIBUTING.md to reflect automated CI instead of manual build verification
• Updated README.md to mention CI coverage and current platform requirements
• Removed outdated "todo" items about GitHub Actions

Benefits

This CI setup provides:

• Automated quality assurance for all code changes
• Multi-platform validation ensuring compatibility across Apple platforms
• Swift Package Manager compliance testing for library consumers
• Modern Swift support (5.10 through 6.0)
• Consistent build environment eliminating "works on my machine" issues

The workflow follows established patterns from leading Swift open source projects, ensuring reliability and maintainability. Contributors and maintainers now have confidence that changes work correctly across supported platforms before merging.

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💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.