tests: ensure kubo is providing cid only once

[guillaumemichel]

Checklist

• My issue is specific & actionable.
• I am not suggesting a protocol enhancement.
• I have searched on the issue tracker for my issue.

Description

kubo is currently writing the same cid multiple times to the provide queue: ipfs/boxo#901

There used to be a mechanism to deduplicate cids before they are provided in boxo/provider, but the mechanism was removed with ipfs/boxo#907

ipfs/boxo#910 is a fix to prevent duplicate cids from being provided multiple times. However, it doubles the internal buffer size of the queue, since it uses a LRU cache to remember and filter out recently provided cids.

This fix wouldn't be required if we can test in kubo that each cid is written once to the provide queue, and only provided once.