Added abstraction layeer IHtmlLoader. Finished reorganizing test project folder structure.

MangaReader.Core/Http/HtmlLoader.cs

@@ -0,0 +1,16 @@
+using HtmlAgilityPack;
+
+namespace MangaReader.Core.Http;
+
+public class HtmlLoader(IHttpService httpService) : IHtmlLoader
+{
+    public async Task<HtmlDocument> GetHtmlDocumentAsync(string url, CancellationToken cancellationToken)
+    {
+        string html = await httpService.GetStringAsync(url, cancellationToken);
+
+        HtmlDocument doc = new();
+        doc.LoadHtml(html);
+
+        return doc;
+    }
+}