don't flush on every body part
Right now we call flush on every body part write, this can be suboptimal, closes #203
Motivation: Library users can write data in small chunk, in this case we are not buffering enough data, better solution would be to buffer at the NIO level in this case.
Modifications:
Body part write is not not flushing, just write
Result: Body part writes are not flushing anymore
Just as a heads up, the main development branch has been changed to main, following the Swift policy on this.
This PR has been re-targeted to main and should just work. However when performing rebases etc please keep this in mind -- you may want to fetch the main branch and rebase onto the main branch from now on since master is not up-to-date anymore and is going to be deleted shortly.