Don't update last page read/read state of chapter if Incognito Mode is enabled

Actually closes #7228, which I forgot was about history more than trackers.

(cherry picked from commit e323f3c25a22ba7b9b831f17064ee7196b5ce951)

# Conflicts:
#	app/src/main/java/eu/kanade/tachiyomi/ui/reader/ReaderViewModel.kt

core/src/main/java/eu/kanade/tachiyomi/util/storage/DiskUtil.kt

@@ -114,4 +114,7 @@ object DiskUtil {
     }
 
     const val NOMEDIA_FILE = ".nomedia"
+
+    // Safe theoretical max filename size is 255 bytes and 1 char = 2-4 bytes (UTF-8)
+    const val MAX_FILE_NAME_BYTES = 250
 }