Make mod loading non nullable, set certain properties to be read only after init (#506)

* Make mod loading non nullable, set certain properties to be read only after init

- Breaks all mods, will require new nugets

* Make mod assembly list IEnumerable

* Convert checks to IsNullOrEmpty

* Update comment, enforce ModGuid

Libraries/SPTarkov.Server.Core/Models/Spt/Mod/AbstractModMetadata.cs

@@ -2,7 +2,7 @@
 
 /// <summary>
 /// Represents a collection of metadata used to determine things such as author, version,
-/// pre-defined load order and incompatibilities. This record is required to be overriden by all mods.
+/// pre-defined load order and incompatibilities. This record is required to be overridden by all mods.
 /// All properties must be overridden. For properties, that you don't need, just assign null.
 /// </summary>
 public abstract record AbstractModMetadata
@@ -13,17 +13,17 @@ public abstract record AbstractModMetadata
     /// It is recommended (but not mandatory) to use
     /// <see href="https://docs.oracle.com/javase/tutorial/java/package/namingpkgs.html">reverse domain name notation</see>.
     /// </summary>
-    public abstract string ModGuid { get; set; }
+    public abstract string ModGuid { get; init; }
 
     /// <summary>
     /// Name of this mod
     /// </summary>
-    public abstract string Name { get; set; }
+    public abstract string Name { get; init; }
 
     /// <summary>
     /// Your username
     /// </summary>
-    public abstract string Author { get; set; }
+    public abstract string Author { get; init; }
 
     /// <summary>
     /// People who have contributed to this mod
@@ -33,12 +33,12 @@ public abstract record AbstractModMetadata
     /// <summary>
     /// Semantic version of this mod, this uses the semver standard
     /// </summary>
-    public abstract string Version { get; set; }
+    public abstract string Version { get; init; }
 
     /// <summary>
     /// SPT version this mod was built for
     /// </summary>
-    public abstract string SptVersion { get; set; }
+    public abstract string SptVersion { get; init; }
 
     /// <summary>
     /// List of mods this mod should load before
@@ -75,5 +75,5 @@ public abstract record AbstractModMetadata
     /// <summary>
     /// Name of the license this mod uses
     /// </summary>
-    public abstract string? Licence { get; set; }
+    public abstract string License { get; init; }
 }