athenad: add threshold to update upload progress

[deanlee]

1. Introduces a threshold for updating upload progress, ensuring updates only occur when progress surpasses the threshold. This reduces unnecessary updates and minimizes lock contention on cur_upload_items.
2. Removes the tid parameter from the callback function. Since the callback is always invoked within the do_upload thread, passing the current item directly enhances clarity and simplifies the code.

While it's uncertain whether this change directly resolves the recently reported issue of "slower upload queue listing and queuing," it remains a valuable improvement for reducing lock contention.

[sshane]

While I appreciate you making these athena correctness changes, the original issue was to root cause the memory leak blocking release. There's been a bit too many subtle or real bugs from these changes, exacerbated by me not having enough time to test each one. Because of that, we should focus on the original issue at hand first instead of fixing real, but so far unnoticed thread safety issues hoping that they might fix the memory leak.