discord.py problem with slash command in cogs

this is should be slash command about bot ping but i didnt understand how write slahs commands in cogs

import discord 
from discord.ext import commands
from discord import Interaction 

client = commands.Bot(command_prefix='#', intents=discord.Intents.all())

class ping(commands.Cog):
    def __init__(self, client):
        self.client = client
    @commands.Cog.listener()
    async def on_ready(self):
        await client.tree.sync()
        print("/ping.py is ready!")

@client.tree.command(name="ping", description="shows bot ping in ms.")
async def ping(self, interaction: discord.Interaction):
    bot_latency = round(self, client.latency * 1000)
    await interaction.response.send_message(f"Pong!{bot_latency} ms.") 


async def setup(client):
    await client.add_cog(ping(client))       

error: TypeError: unsupported type annotation <class 'discord.interactions.Interaction'>

help pls, i dont even close understand where is the problem

Your command is out of the cog and also, you are using client.tree.command, that decorator is only available outside cogs, in the main file. For cogs must use app_commands.command decorator.
Also, try to use cog classes outside the main file to prevent errors.

import discord
from discord.ext import commands
from discord import app_commands
from discord import Interaction

# This must be in your main file, not in the cog one
client = commands.Bot(..)

# This must be in another file
class Ping(commands.Cog):
    # __init__ is unnecessary, the class auto applies the client parameter
    @commands.Cog.listener()
    async def on_ready(self):
        ...

    @app_commands.command(description = "Shows bot current latency in ms.")
    async def ping(self, interaction:discord.Interaction):
        bot_latency = round(self.client.latency * 1000) # here you can also use interaction.client.latency instead of self.client.latency
        await interaction.response.send_message(f"Pong! Bot latency is `{bot_latency}`ms")

async def setup(client):
    await client.add_cog(Ping(client))