Allow downloading attachments into memory

[imrehg]

The current download_attachment method always has to write to file:

jmapc/jmapc/client.py

Lines 151 to 170 in f8200fa

	def download_attachment(
	self,
	attachment: EmailBodyPart,
	file_name: Union[str, Path],
	) -> None:
	if not file_name:
	raise Exception("Destination file name is required")
	file_name = Path(file_name)
	blob_url = self.jmap_session.download_url.format(
	accountId=self.account_id,
	blobId=attachment.blob_id,
	name=attachment.name,
	type=attachment.type,
	)
	r = self.requests_session.get(
	blob_url, stream=True, timeout=REQUEST_TIMEOUT
	)
	r.raise_for_status()
	with open(file_name, "wb") as f:
	f.write(r.raw.data)

It would be handy to optionally write to memory, ie. being able to use io.BytesIO objects. This would make the library more flexible to be used as a library. A use case being for example an ETL tool that processes the contents of email attachments.

I'm happy to contribute as well.

[Dacid99]

I felt the same way and made a PR for this (#124). Unfortunately I don't know whether it will ever be merged, as there has been no activity for the better part of a year ..