Fix numeric deck and notetype names being treated as ids when importing csv

[iamllama]

Reported in https://forums.ankiweb.net/t/import-problem-deck-field-is-ignored-since-version-24-11

Fixes numeric deck and notetype names being treated as ids in #deck:..., or in the specified deck/notetype column

DeckIdsByNameOrId::get, Collection::deck_id_by_name_or_id and Collection::notetype_by_name_or_id are modified to fallback to treating ids as names if said deck/notetype id is nonexistent

Modifying Collection.deck_id_by_name_or_id may seem redundant, as the metadata deck goes through DeckIdsByNameOrId::get anyway, but since its used by the import options page, it's kept for consistency when dealing with #deck:<numeric>

The only breakage I can think of is when an exporter exports notes from a deck with a name that's the same as one of the importer's decks' ids, in which case the deck with that id would be used instead of making a new deck with the id as the name. But this seems highly pathological, and is identical to existing behaviour regardless.

[dae]

Another good change - thanks again!