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/Serialization/IGenericReader.cs

@@ -26,6 +26,8 @@ public interface IGenericReader
     DateTime LastSerialized { get; init; }
 
     string ReadString(bool intern = false);
+    public string ReadStringRaw(bool intern = false);
+
     long ReadLong();
     ulong ReadULong();
     int ReadInt();