Track when we enqueue logs for the same upkeep on the same block more than once

[ferglor]

https://smartcontract-it.atlassian.net/browse/AUTO-10164

WIth this PR, we're updating some comments within the buffer implementation, to explicitly declare our assumptions on how the buffer will be used.

Further to this, we're also adding logs to identify scenarios when these assumptions are violated. To achieve this, we use a map to track the number of times we enqueue upkeep logs for a particular block number.

Testing

Running the load test, we don't see the logs appear for enqueuing upkeep logs for the same block number more than once.

[cl-sonarqube-production[bot]]

Quality Gate passed

Issues
0 New issues
0 Fixed issues
0 Accepted issues

Measures
0 Security Hotspots
No data about Coverage
0.0% Duplication on New Code

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