Feat: migrate to Java NIO

[EchoEllet]

The project previously used a mix between java.nio and java.io packages, usually, it uses File (java.io) or Paths and Files (java.nio)

This migrates to use Path as a new alternative of java.io.File, Kotlin has built-in extensions to use Files functions directly in Path, java.nio depends on java.io and uses some classes such as java.io.IOException

Some other usages might have alternatives through some classes such as HttpExchange still use them:

import java.io.*;
import java.nio.*;

Java uses a mix of both java.io and java.nio for compatibility.

The error message and error handling have been improved.