Adds a wall timeout `image_download_max_timeout` to enforce an upper
bound on total download duration.
While the per-chunk timeout protects against stalled reads, downloads
that trickle in just under the timeout threshold (e.g., due to heavy
TCP retransmits) can hang for longer than intended.
Now, if the total allowed time is exceeded, the download is aborted with
a non-retryable `ImageDownloadTimeoutError` regardless of per-chunk
retry or connection success.
A value of 0 (the default) disables this feature.
Closes-Bug: #2115995
Change-Id: I3b56d21abae0488853bfed14072ba21116d47baf
Signed-off-by: Afonne-CID <afonnepaulc@gmail.com>
e1a31eb97a