fix: Reverts GetAccount to use IAccount. Adds IAccount to serialization. (#1565)

### Summary

- Fixes usernames not being `Intern`ed
- Reverts methods related to getting accounts from returning `Account` to `IAccount`.
- Makes `IAccount` also `ISerializable`
- Adds `IGenericReader.ReadAccount()` and `IGenericWriter.Write(IAccount)` -> The read method supports the original serialization of username, and using `IAccount.Serial`. The write method only serializes the `Serial`.
- Exposes `ReadStringRaw()` to allow some advanced scenarios.

Projects/Server.Tests/Tests/Network/Packets/Outgoing/AccountPacketTests.cs

@@ -47,15 +47,19 @@ public class AccountPacketTests : IClassFixture<ServerFixture>
             }
         }
 
-        public void Delete()
-        {
-            throw new NotImplementedException();
-        }
+        public DateTime Created { get; set; }
+        public long SavePosition { get; set; }
+        public BufferWriter SaveBuffer { get; set; }
+        public Serial Serial { get; }
+        public void Deserialize(IGenericReader reader) => throw new NotImplementedException();
 
-        public void SetPassword(string password)
-        {
-            throw new NotImplementedException();
-        }
+        public void Serialize(IGenericWriter writer) => throw new NotImplementedException();
+
+        public bool Deleted { get; }
+
+        public void Delete() => throw new NotImplementedException();
+
+        public void SetPassword(string password) => throw new NotImplementedException();
 
         public bool CheckPassword(string password) => throw new NotImplementedException();
     }