Let fetchSSHAction own the per-fetch deadline and pass the connection cancellation context directly from clientAuth. Remove the duplicate timeout and its deferred cancellation inside the action loop. Derive the longer transport watchdog from the fetch timeout, keeping both durations unchanged.
Use virtual time to test the fetch deadline across retries, earlier parent deadlines, and parent cancellation. Verify that a successful fetch releases its request context.
Updates tailscale/corp#50380
Change-Id: I185958ca19566f04cbd68f33e4b1dad3d18aebb7
Signed-off-by: James Tucker <james@tailscale.com>
