Fixing parsing yaml files when settings or build gradle files are not inlcuded

[cdsap]

Introduce VersionsFile for YAML parsing of additional settings and root build plugins.

This fixes a bug where omitting additionalSettingsPlugins or additionalBuildGradleRootPlugins from versions.yaml still applied the default Spotlight and dependency-analysis plugins. Versions remains the resolved runtime model with defaults, while VersionsFile now represents YAML overrides and resolves omitted plugin lists to empty.

Changes

• add VersionsFile as the YAML-facing config model
• resolve omitted plugin list fields to emptyList()
• update VersionsParser to parse VersionsFile and convert to Versions
• remove the custom deserializer workaround
• add tests for parser and resolver behavior