perf(misc): use arrays instead of slices where possible

Arrays have a fixed size in go, while slices don't, making the former way
faster than the latter: https://go-benchmarks.com/array-vs-slice

internal/reader/processor/reading_time.go

@@ -65,7 +65,7 @@ func updateEntryReadingTime(store *storage.Storage, feed *model.Feed, entry *mod
 	}
 
 	// Define watch time fetching scenarios
-	watchTimeScenarios := []struct {
+	watchTimeScenarios := [...]struct {
 		shouldFetch func(*model.Entry) bool
 		fetchFunc   func(string) (int, error)
 		platform    string