Perform download cache renewal async

Don't block on cache renewals, but notify library on updates so that the badges show up when ready.

We skip the cache when checking if a chapter is downloaded for the reader assuming that it's a
relatively low cost to check for a single chapter.

(Probably) fixes #8254 / fixes #7847

app/src/main/java/eu/kanade/tachiyomi/source/SourceManager.kt

@@ -113,7 +113,7 @@ class SourceManager(
     }
 
     @Suppress("OverridingDeprecatedMember")
-    open inner class StubSource(val sourceData: SourceData) : Source {
+    open inner class StubSource(private val sourceData: SourceData) : Source {
 
         override val id: Long = sourceData.id
 
@@ -125,6 +125,7 @@ class SourceManager(
             throw getSourceNotInstalledException()
         }
 
+        @Deprecated("Use the 1.x API instead", replaceWith = ReplaceWith("getMangaDetails"))
         override fun fetchMangaDetails(manga: SManga): Observable<SManga> {
             return Observable.error(getSourceNotInstalledException())
         }
@@ -133,6 +134,7 @@ class SourceManager(
             throw getSourceNotInstalledException()
         }
 
+        @Deprecated("Use the 1.x API instead", replaceWith = ReplaceWith("getChapterList"))
         override fun fetchChapterList(manga: SManga): Observable<List<SChapter>> {
             return Observable.error(getSourceNotInstalledException())
         }
@@ -141,6 +143,7 @@ class SourceManager(
             throw getSourceNotInstalledException()
         }
 
+        @Deprecated("Use the 1.x API instead", replaceWith = ReplaceWith("getPageList"))
         override fun fetchPageList(chapter: SChapter): Observable<List<Page>> {
             return Observable.error(getSourceNotInstalledException())
         }