cmd/uplink: fix progressbar data race

[egonelbre]

There was a data race in the old version version of cheggaaa/pb, use a newer version. Also ensure that the bar has always been finished before we return.

Based on issue reports and commit history, this should fix it, however since there isn't a good reproducer, it's not entirely clear whether it completely fixes it or not.

Please describe the tests:

• Test 1:
• Test 2:

Please describe the performance impact:

Code Review Checklist (to be filled out by reviewer)

• Does the PR describe what changes are being made?
• Does the PR describe why the changes are being made?
• Does the code follow our style guide?
• Does the code follow our testing guide?
• Is the PR appropriately sized? (If it could be broken into smaller PRs it should be)
• Does the new code have enough tests? (every PR should have tests or justification otherwise. Bug-fix PRs especially)
• Does the new code have enough documentation that answers "how do I use it?" and "what does it do?"? (both source documentation and higher level, diagrams?)
• Does any documentation need updating?
• Do the database access patterns make sense?

[mniewrzal]

• Does the PR describe what changes are being made?
• Does the PR describe why the changes are being made?
• Does the code follow our style guide?
• Does the code follow our testing guide?
• Is the PR appropriately sized? (If it could be broken into smaller PRs it should be)
• Does the new code have enough tests? (every PR should have tests or justification otherwise. Bug-fix PRs especially)
• Does the new code have enough documentation that answers "how do I use it?" and "what does it do?"? (both source documentation and higher level, diagrams?)
• Does any documentation need updating?
• Do the database access patterns make sense?

[stefanbenten]

LGTM. Does the new progress bar not need the specification of width and units?

[egonelbre]

@stefanbenten when you use NewProxyReader it will automatically switch to bytes mode.