Make resource-fetching methods of clients return `DavResource[WithChildren]` objects

[jwodder]

• The following methods should be modified to return DavResource or DavResourceWithChildren objects, as appropriate:

  • DandiClient::get_all_dandisets()
  • DandisetEndpoint::get()
  • DandisetEndpoint::get_all_versions()
  • VersionEndpoint::get()
  • VersionEndpoint::get_metadata()
  • VersionEndpoint::get_resource()
  • VersionEndpoint::get_resource_with_children()
  • VersionEndpoint::get_root_children()
  • ZarrManClient::get_top_level_dirs()
  • ZarrManClient::get_resources()
  • ZarrManClient::get_resources_with_children()

• The types that the above methods currently return should all have their visibilities restricted to crate::dandi or crate::zarrman, as appropriate

• Various types in src/zarrman/resources.rs should then be renamed for greater accuracy (made easier by the fact that these types no longer have to coexist alongside crate::dandi types):

  • Manifest → Zarr
  • ManifestFolder → ZarrFolder
  • ManifestEntry → ZarrEntry

  and likewise for enum variants