feat(readarr): add the indexers handlers

Add IndexersHandler and its three sub-handlers, EditIndexerHandler, IndexerSettingsHandler and TestAllIndexersHandler, and dispatch to them from ReadarrHandler.

IndexersHandler::accepts ORs in all three children, so the parent and the children land together. Splitting would leave eighteen blocks accepted but inert, with Esc falling through to handle_clear_errors instead of popping.

TestAllIndexersHandler::accepts compares the block for equality rather than consulting an array, since TestAllIndexers appears in no block array.

src/handlers/readarr_handlers/readarr_handler_tests.rs

@@ -247,6 +247,30 @@ mod tests {
     );
   }
 
+  #[rstest]
+  fn test_delegates_indexers_blocks_to_indexers_handler(
+    #[values(
+      ActiveReadarrBlock::Indexers,
+      ActiveReadarrBlock::DeleteIndexerPrompt,
+      ActiveReadarrBlock::TestIndexer,
+      ActiveReadarrBlock::TestAllIndexers,
+      ActiveReadarrBlock::EditIndexerPrompt,
+      ActiveReadarrBlock::AllIndexerSettingsPrompt,
+      ActiveReadarrBlock::IndexerSettingsConfirmPrompt,
+      ActiveReadarrBlock::IndexerSettingsMaximumSizeInput,
+      ActiveReadarrBlock::IndexerSettingsMinimumAgeInput,
+      ActiveReadarrBlock::IndexerSettingsRetentionInput,
+      ActiveReadarrBlock::IndexerSettingsRssSyncIntervalInput
+    )]
+    active_readarr_block: ActiveReadarrBlock,
+  ) {
+    test_handler_delegation!(
+      ReadarrHandler,
+      ActiveReadarrBlock::Indexers,
+      active_readarr_block
+    );
+  }
+
   #[rstest]
   fn test_delegates_system_blocks_to_system_handler(
     #[values(