Updates go-proton-api and Gluon to includes memory reduction changes and
modify the sync process to take into account how much memory is used
during the sync stage.
The sync process now has an extra stage which first download the message
metada to ensure that we only download up to `syncMaxDownloadRequesMem`
messages or 250 messages total. This allows for scaling the download
request automatically to accommodate many small or few very large
messages.
The IDs are then sent to a download go-routine which downloads the
message and its attachments. The result is then forwarded to another
go-routine which builds the actual message. This stage tries to ensure
that we don't use more than `syncMaxMessageBuildingMem` to build these
messages.
Finally the result is sent to a last go-routine which applies the
changes to Gluon and waits for them to be completed.
The new process is currently limited to 2GB. Dynamic scaling will be
implemented in a follow up. For systems with less than 2GB of memory we
limit the values to a set of values that is known to work.
This fixes various race conditions and leaks related to the user's sync
and API event stream. It was possible for a sync/stream to begin after a
user was already closed; this change prevents that by managing the
goroutines related to sync/stream within cancellable groups.
