refactor!: Snapshot should not expose delta implementation details

[OussamaSaoudi]

Currently, the Snapshot struct has pub methods to access protocol, metadata, and column_mapping_mode. These methods are Delta implementation details that are best not exposed to the user. A Snapshot user should only be interested in the version and the schema. On the other hand, consumers of kernel may need to know more things about the table such as table configuration. Thus we need a way to make these internal details public. Kernel allows this through the developer-visibility feature flag.

Remove the methods protocol, metadata, and column_mapping methods from Snapshot. Change all callers so that they use table_configuration() instead.