Fix MAL error when list entries have partial dates (#3573)

This has the side effect of forcing the date to something concrete.

For Year-only: 1st of January that year
Ex: 2025 -> 2025-01-01

For Year+Month: 1st of said month
Ex: 2024-11 -> 2024-11-01

MAL allows setting Day+Month and Day+Year, but both of those are sent
as `null` in the API, which means Mihon will not show a date at all.
This has the side effect of Mihon sending up the date as `null` the
next time info is sent to MAL, which will clear the date fields
completely.

Co-authored-by: AntsyLich <59261191+AntsyLich@users.noreply.github.com>

app/src/main/java/eu/kanade/tachiyomi/data/track/myanimelist/MyAnimeListApi.kt

@@ -245,7 +245,13 @@ class MyAnimeListApi(
     }
 
     private fun parseDate(isoDate: String): Long {
-        return SimpleDateFormat("yyyy-MM-dd", Locale.US).parse(isoDate)?.time ?: 0L
+        val pattern = when (isoDate.length) {
+            10 -> "yyyy-MM-dd"
+            7 -> "yyyy-MM"
+            4 -> "yyyy"
+            else -> throw IllegalArgumentException("Unsupported date format: \"$isoDate\"")
+        }
+        return SimpleDateFormat(pattern, Locale.US).parse(isoDate)?.time ?: 0L
     }
 
     private fun convertToIsoDate(epochTime: Long): String? {