Add local TBA file downloading

[LasterAlex]

Inspired by https://t.me/teloxide/22547

Made it just because it was quick and I could, if it seems useful - would be glad to see this merged, but it's not very important

Code snippet to test this:

use std::str::FromStr;

use teloxide::{
    dispatching::{UpdateFilterExt, UpdateHandler},
    net::Download,
    prelude::*,
};

type HandlerResult = Result<(), Box<dyn std::error::Error + Send + Sync>>;

async fn download_document(bot: Bot, message: Message) -> HandlerResult {
    if let Some(document) = message.document() {
        let file = bot.get_file(document.file.id.clone()).await?;
        let mut dest = tokio::fs::File::create("test.txt").await?;
        bot.download_file(&file.path, &mut dest).await?;

        assert!(tokio::fs::read_to_string("test.txt").await.is_ok());

        bot.send_message(message.chat.id, "Downloaded!").await?;

        tokio::fs::remove_file("test.txt").await?;
    } else {
        bot.send_message(message.chat.id, "Not a document").await?;
    }
    Ok(())
}

fn handler_tree() -> UpdateHandler<Box<dyn std::error::Error + Send + Sync + 'static>> {
    dptree::entry().branch(Update::filter_message().endpoint(download_document))
}

#[tokio::main]
async fn main() {
    let bot = Bot::from_env().set_api_url(reqwest::Url::from_str("http://localhost:8081").unwrap());

    Dispatcher::builder(bot, handler_tree())
        .enable_ctrlc_handler()
        .build()
        .dispatch()
        .await;
}

Cargo.toml:

[dependencies]
teloxide = { git = "https://github.com/LasterAlex/teloxide", branch = "add-local-file-downloading"}
tokio = { version = "1.38", features = ["rt-multi-thread", "macros"] }
reqwest = "0.12.7"

Just send a .txt file to this bot

[teloxidebot]

r? @hirrolot

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