feat(itch): collections filter in the Library (#1597)

* Add itch.io collections to the Library

A Collections button on the Library's itch tab filters the library to one collection of the signed-in account. Its games that are not installed show in the Not installed section.

* Keep itch collections complete across failures, sign-out and empty libraries

A failed later page no longer publishes a partial collection, selecting a collection refreshes it, pagination runs until an empty page, signing out clears collection state, and the itch chip shows for a signed-in account with no owned games.

* Tie itch collection requests to the account that started them

Requests capture the account generation before reading the key and dedupe per generation, sign-out clears collections after the token is removed, and the collections load follows the itch sign-in state.

* Keep paging itch collections past a page of already seen games

* Run the itch collections tests under Robolectric like the other itch tests

* Let the Installed filter apply inside a collection and keep the grid for an empty itch account

* fix(itch): stop paging a collection when a page adds no new games

* Keep the collections icon on the itch collections tab when it opens

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Co-authored-by: maxjivi05 <maxjividen@gmail.com>

docs/development/itch-collections.md

@@ -0,0 +1,26 @@
+# itch.io collections
+
+On the Library's itch tab a Collections button in the header lists the collections of the signed-in
+itch account. Picking one hides every game that is not in it; the games of the collection that are not
+installed show in the existing "Not installed" section, and All brings the full library back. The button
+exists only while the itch chip is selected.
+
+## Data
+
+`ItchCollections` (`stores/itch/ItchCollections.kt`) asks itch with the account's API key:
+
+```
+GET /profile/collections                          -> collections[{id, title, games_count}]
+GET /collections/<id>/collection-games?page=N     -> collection_games[{game{...}}]
+```
+
+Pages are read until one comes back empty. Each game goes through `ItchLibrary.item`, the reader the
+library and shelves share, so it looks the same everywhere. The selection and the loaded games live in
+memory; the list is asked again whenever the itch tab opens. Counts are logged
+(`itch.io: <n> collections`, `itch.io: collection <id> has <n> games`).
+
+## Filtering
+
+`collectionEntries` keeps the itch entries whose store key is in the collection, then adds the
+collection games the library has no entry for as not installed ones. Their game page resolves through
+`StoresState.detailItem`, which also looks at the collection games.