Update pandocast for pandoc-types 1.23 (Pandoc 3.1)

[Omikhleia]

Implicit figures have apparently changed in pandoc 3.1 (based on pandoc-types 1.23), generating something such as:

[ Figure
    ( "" , [] , [] )
    (Caption Nothing [ Plain [ Str "text" ] ])
    [ Plain
        [ Image
            ( "" , [] , [] ) [ Str "text" ] ( "uri" , "" )
        ]
    ]
]

.... Instead of a Para with an Image.

I haven't checked yet -- it might relate (or not) to the implicit_figures extension.

We'd need to check and possibly update the pandocast inputter to support the change.