feat: make attachment downloading chunkable

[hzhreal]

Summary

The point of this PR is to offer an option for developers to download attachments in chunks instead of processing the whole file in memory at once to reduce possible overhead.

Changes:

• Add the method HTTPClient.get_from_cdn_stream that yields data in chunks
• Add the method Attachment.read_chunked to process data in chunks
• Modify the method Attachment.save giving the option to write data to a file in chunks through an optional parameter

Information

• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed).
• This PR is not a code change (e.g. documentation, README, typehinting,
  examples, ...).

Checklist

• I have searched the open pull requests for duplicates.
• If code changes were made then they have been tested.
• I have updated the documentation to reflect the changes.
• If type: ignore comments were used, a comment is also left explaining why.
• I have updated the changelog to include these changes.

[pycord-app]

Thanks for opening this pull request!
Please make sure you have read the Contributing Guidelines and Code of Conduct.

This pull request can be checked-out with:

git fetch origin pull/2956/head:pr-2956
git checkout pr-2956

This pull request can be installed with:

pip install git+https://github.com/Pycord-Development/pycord@refs/pull/2956/head

[hzhreal]

Test code:

import discord
import os
import aiofiles
from discord.ext import commands

bot = commands.Bot()

CHUNKSIZE = 1024 * 1024

@bot.slash_command()
async def download(ctx: discord.ApplicationContext, f: discord.Attachment) -> None:
    size = f.size
    written = 0
    progress = "{}/{}"
    await ctx.respond(progress.format(written, size))
    async with aiofiles.open("test1.bin", "wb") as out:
        async for chunk in f.read_chunked(chunksize=CHUNKSIZE):
            await out.write(chunk)
            chunksize = len(chunk)
            written += chunksize
            await ctx.edit(content=progress.format(written, size))
    await f.save("test2.bin", chunksize=chunksize)

bot.run(os.getenv("TOKEN"))

[Paillat-dev]

@hzhreal Could you please fix the merge conflicts ? Thx

done