[fix] more robust search and error for MLD binary

import math

import multiprocessing as mp

import platform

import shutil

import subprocess

import tempfile

from pathlib import Path

                mld = toolsdir.joinpath(platform.system()).joinpath("mld")

            else:

                assert False, f"MLD tool not available for {platform.system()}"

            if not mld.exists():

                mld = shutil.which("mld")

                search_path = toolsdir.joinpath(platform.system().replace("Windows", "Win32"))

                if mld is None:

                    assert False, f"MLD tool not found in {search_path} or PATH!"

                warnings.warn(f"MLD binary not found in {search_path}! Falling back to {mld}!")

            with tempfile.TemporaryDirectory() as tmpdir:

                for i in range(nchannels):