Recognize merged part-chapters as new chapters

For example:
ch2 1.zip
ch2 2.zip
Kavita will merge these into one big ch2.
Recognize and handle chapter merges.

src/all/kavita/src/eu/kanade/tachiyomi/extension/all/kavita/Kavita.kt

@@ -513,11 +513,14 @@ class Kavita(private val suffix: String = "") : ConfigurableSource, UnmeteredSou
      * Fetches the "url" of each page from the chapter
      * **/
     override fun pageListRequest(chapter: SChapter): Request {
-        return GET("$apiUrl/${chapter.url}", headersBuilder().build())
+        // remove potential _<part> chapter salt
+        val chapterId = chapter.url.substringBefore("_")
+        return GET("$apiUrl/$chapterId", headersBuilder().build())
     }
 
     override fun fetchPageList(chapter: SChapter): Observable<List<Page>> {
-        val chapterId = chapter.url
+        // remove potential _<part> chapter salt
+        val chapterId = chapter.url.substringBefore("_")
         val numPages = chapter.scanlator?.replace(" pages", "")?.toInt()
         val numPages2 = "$numPages".toInt() - 1
         val pages = mutableListOf<Page>()

src/all/kavita/src/eu/kanade/tachiyomi/extension/all/kavita/KavitaHelper.kt

@@ -98,6 +98,13 @@ class KavitaHelper {
             }
 
             url = chapter.id.toString()
+
+            if (chapter.fileCount > 1) {
+                // salt/offset to recognize chapters with new merged part-chapters as new and hence unread
+                chapter_number += 0.001f * chapter.fileCount
+                url = "${url}_${chapter.fileCount}"
+            }
+
             date_upload = parseDate(chapter.created)
             scanlator = "${chapter.pages} pages"
         }

src/all/kavita/src/eu/kanade/tachiyomi/extension/all/kavita/dto/MangaDto.kt

@@ -123,4 +123,13 @@ data class ChapterDto(
     val coverImageLocked: Boolean,
     val volumeId: Int,
     val created: String,
+    val files: List<FileDto>? = null,
+) {
+    val fileCount: Int
+        get() = files?.size ?: 0
+}
+
+@Serializable
+data class FileDto(
+    val id: Int,
 )