Add Release Build GitHub Action

[swlodarski-sumoheavy]

Adds a new GitHub Actions workflow that automatically builds and packages the BitPay NuGet package for release when a new GitHub release is published.

What's Changed

• New workflow: release.yml
  • Triggered automatically when a GitHub release is published
  • Runs on Windows 2022 to support all target frameworks
• Bump version to 6.0.1

Features

• Multi-target build: Compiles the library for all supported frameworks:
  • .NET Framework 4.8 (net48)
  • .NET 8.0 (net8.0)
  • .NET 9.0 (net9.0)
• Test validation: Runs unit tests across all supported test frameworks before packaging
• NuGet artifact creation:
  • Creates multi-targeted NuGet package (.nupkg) containing binaries for all frameworks
  • Generates symbol package (.snupkg) for debugging support
  • Uploads both as workflow artifacts with 90-day retention

Usage

1. Create a new GitHub release from the Releases page
2. The workflow will automatically trigger and build the package
3. Download the NuGet package from the workflow run's artifacts

Benefits

• Ensures consistent, reproducible builds for releases
• Validates all tests pass before packaging
• Provides downloadable artifacts for manual verification before publishing to NuGet.org
• Single package contains all target framework versions