[liubquanti]

Fix AniList library parsing and list updates

Since #2952 (migration to kotlinx serialization) AniList sync is broken in two ways.

1. Library list fails to load

Jackson used to coerce null into 0 for non-nullable Int fields, kotlinx does not.
AniList returns null for completedAt / startedAt dates of any entry that isn't
completed, as well as episodes (airing shows) and seasonYear (unannounced shows), so
getFullAniListList fails on practically every account:

Unexpected JSON token at offset 116: Unexpected symbol 'n' in numeric literal at path:
$.data.MediaListCollection.lists[0].entries[0].completedAt.year

These fields are now nullable. StartedAt fields are Int? to match AniList's
FuzzyDate type (they were String?, but AniList sends numbers).

2. Adding / updating titles silently fails

SaveMediaListEntry always passes scoreRaw: $scoreRaw, progress: $progress, but only
declares those variables when they are non-null. When no score is set AniList rejects the
whole mutation:

Variable "$scoreRaw" is not defined.
Variable "$progress" is not defined.

postDataAboutId only checked data != "", so the failure was reported as success.
Now only the variables that have a value are declared and passed, and a response
containing GraphQL errors is logged and returns false.

Testing

• Added AniListParsingTest covering a list response with null dates/episodes and
  GraphQL error detection.
• Verified the broken mutation against the live AniList API.
• Tested on a Chromecast with Google TV (Android 14): the AniList library tab loads
  again, and status updates without a score now reach AniList.