.NET 7 + Spring Cleaning (#1677)

* Updated to net7.0

* Updated GA to .net 7

* Updated System.IO.Abstractions to use New factory.

* Converted Regex into SourceGenerator in Parser.

* Updated more regex to source generators.

* Enabled Nullability and more regex changes throughout codebase.

* Parser is 100% GeneratedRegexified

* Lots of nullability code

* Enabled nullability for all repositories.

* Fixed another unit test

* Refactored some code around and took care of some todos.

* Updating code for nullability and cleaning up methods that aren't used anymore. Refctored all uses of Parser.Normalize() to use new extension

* More nullability exercises. 500 warnings to go.

* Fixed a bug where custom file uploads for entities wouldn't save in webP.

* Nullability is done for all DTOs

* Fixed all unit tests and nullability for the project. Only OPDS is left which will be done with an upcoming OPDS enhancement.

* Use localization in book service after validating

* Code smells

* Switched to preview build of swashbuckle for .net7 support

* Fixed up merge issues

* Disable emulate comic book when on single page reader

* Fixed a regression where double page renderer wouldn't layout the images correctly

* Updated to swashbuckle which support .net 7

* Fixed a bad GA action

* Some code cleanup

* More code smells

* Took care of most of nullable issues

* Fixed a broken test due to having more than one test run in parallel

* I'm really not sure why the unit tests are failing or are so extremely slow on .net 7

* Updated all dependencies

* Fixed up build and removed hardcoded framework from build scripts. (this merge removes Regex Source generators). Unit tests are completely busted.

* Unit tests and code cleanup. Needs shakeout now.

* Adjusted Series model since a few fields are not-nullable. Removed dead imports on the project.

* Refactored to use Builder pattern for all unit tests.

* Switched nullability down to warnings. It wasn't possible to switch due to constraint issues in DB Migration.

API/Entities/Series.cs

@@ -12,27 +12,27 @@ public class Series : IEntityDate, IHasReadTimeEstimate
     /// <summary>
     /// The UI visible Name of the Series. This may or may not be the same as the OriginalName
     /// </summary>
-    public string Name { get; set; }
+    public required string Name { get; set; }
     /// <summary>
     /// Used internally for name matching. <see cref="Services.Tasks.Scanner.Parser.Parser.Normalize"/>
     /// </summary>
-    public string NormalizedName { get; set; }
+    public required string NormalizedName { get; set; }
     /// <summary>
     /// Used internally for localized name matching. <see cref="Services.Tasks.Scanner.Parser.Parser.Normalize"/>
     /// </summary>
-    public string NormalizedLocalizedName { get; set; }
+    public required string NormalizedLocalizedName { get; set; }
     /// <summary>
     /// The name used to sort the Series. By default, will be the same as Name.
     /// </summary>
-    public string SortName { get; set; }
+    public required string SortName { get; set; }
     /// <summary>
     /// Name in original language (Japanese for Manga). By default, will be same as Name.
     /// </summary>
-    public string LocalizedName { get; set; }
+    public required string LocalizedName { get; set; }
     /// <summary>
     /// Original Name on disk. Not exposed to UI.
     /// </summary>
-    public string OriginalName { get; set; }
+    public required string OriginalName { get; set; }
     /// <summary>
     /// Time of creation
     /// </summary>
@@ -49,7 +49,7 @@ public class Series : IEntityDate, IHasReadTimeEstimate
     /// Absolute path to the (managed) image file
     /// </summary>
     /// <remarks>The file is managed internally to Kavita's APPDIR</remarks>
-    public string CoverImage { get; set; }
+    public string? CoverImage { get; set; }
     /// <summary>
     /// Denotes if the CoverImage has been overridden by the user. If so, it will not be updated during normal scan operations.
     /// </summary>
@@ -62,7 +62,7 @@ public class Series : IEntityDate, IHasReadTimeEstimate
     /// Highest path (that is under library root) that contains the series.
     /// </summary>
     /// <remarks><see cref="Services.Tasks.Scanner.Parser.Parser.NormalizePath"/> must be used before setting</remarks>
-    public string FolderPath { get; set; }
+    public string? FolderPath { get; set; }
     /// <summary>
     /// Last time the folder was scanned
     /// </summary>
@@ -96,22 +96,22 @@ public class Series : IEntityDate, IHasReadTimeEstimate
     public int MaxHoursToRead { get; set; }
     public int AvgHoursToRead { get; set; }
 
-    public SeriesMetadata Metadata { get; set; }
+    public SeriesMetadata Metadata { get; set; } = null!;
 
-    public ICollection<AppUserRating> Ratings { get; set; } = new List<AppUserRating>();
-    public ICollection<AppUserProgress> Progress { get; set; } = new List<AppUserProgress>();
+    public ICollection<AppUserRating> Ratings { get; set; } = null!;
+    public ICollection<AppUserProgress> Progress { get; set; } = null!;
 
     /// <summary>
     /// Relations to other Series, like Sequels, Prequels, etc
     /// </summary>
     /// <remarks>1 to Many relationship</remarks>
-    public virtual ICollection<SeriesRelation> Relations { get; set; } = new List<SeriesRelation>();
-    public virtual ICollection<SeriesRelation> RelationOf { get; set; } = new List<SeriesRelation>();
+    public ICollection<SeriesRelation> Relations { get; set; } = null!;
+    public ICollection<SeriesRelation> RelationOf { get; set; } = null!;
 
 
     // Relationships
-    public List<Volume> Volumes { get; set; }
-    public Library Library { get; set; }
+    public List<Volume> Volumes { get; set; } = null!;
+    public Library Library { get; set; } = null!;
     public int LibraryId { get; set; }
 
     public void UpdateLastFolderScanned()