• Added tagPattern and version fields to GitDependency, to support the
  tag_pattern key for git dependencies introduced in Dart 3.9.
• Added a usage example.
• Fix Pubspec.fromJson with lenient: true to preserve the input Map
  (YamlMap) when name is invalid or missing.
• Preserve nested Map (YamlMap) keys and spans when git or hosted
  dependency shorthands fail to parse or when Pubspec.fromJson is called with
  a non-YamlMap Map.
• Added fields to Pubspec: falseSecrets, hooks, platforms.
• Added version to PathDependency, exposing the constraint from an
  accompanying version key instead of silently discarding it.