OPDS Enhancements, Epub fixes, and a lot more (#4035)

Co-authored-by: Amelia <77553571+Fesaa@users.noreply.github.com>
Co-authored-by: Robbie Davis <robbie@therobbiedavis.com>
Co-authored-by: Fabian Pammer <fpammer@mantro.net>
Co-authored-by: Vinícius Licz <vinilicz@gmail.com>

API/Extensions/StringExtensions.cs

@@ -1,5 +1,6 @@
 using System;
 using System.Globalization;
+using System.Linq;
 using System.Text.RegularExpressions;
 
 namespace API.Extensions;
@@ -81,4 +82,15 @@ public static class StringExtensions
         return input[0] + new string('*', atIdx - 1) + input[atIdx..];
     }
 
+    /// <summary>
+    /// Repeat returns a string that is equal to the original string repeat n times
+    /// </summary>
+    /// <param name="input">String to repeat</param>
+    /// <param name="n">Amount of times to repeat</param>
+    /// <returns></returns>
+    public static string Repeat(this string? input, int n)
+    {
+        return string.IsNullOrEmpty(input) ? string.Empty : string.Concat(Enumerable.Repeat(input, n));
+    }
+
 }