Add new Packagist API properties

[robbieaverill]

#92 reports that new Packagist API properties that are added, which were being assigned dynamically in AbstractResult, are causing deprecation warnings in PHP 8.2. #96 makes a change to ignore dynamic properties.

We should add the new properties we know about, so they can be used by consumers:

• Package
  • githubWatchers
  • githubOpenIssues
  • language
• Package/Version
  • support
  • targetDir
  • defaultBranch
• Package/Maintainer
  • avatarUrl

Ideally the updates API fixtures contain real-world examples from the Packagist API for these properties.