ConsumeCompleted -> ConsumeCompletedIn

[rukai]

Previously we allowed for measuring the throughput of consumption but not the latency.
This was because it wasnt clear to me how to define latency for consumption.

I am comparing the results of windsock benchmarks against the results of the https://github.com/confluentinc/librdkafka/blob/master/examples/rdkafka_performance.c tool which another team uses for measuring shotover + kafka performance.
I investigated how rdkafka_performance measures latency of consumption:
It stores a timestamp in the record payload at produce time and then compares the payload against the current time at consume time.
This approach makes a lot of sense and we should enable use of this approach in windsock.

This PR adds infrastructure to windsock for measuring consumption latency.
The logic for measuring consumption latency mirrors that of producing latency with one exception:
The durations passed to windsock in Report::ConsumeCompletedIn are an Option<Duration> instead of just Duration. This allows a None to be passed in the case where the benchmark is testing a payload size so small that it cannot fit a timestamp.

Since consumer latency can be None, I took the opportunity to allow the intermediate layers of the producer latency logic to store latency as None. This is used when no messages were sent during the bench, in this case it will now display the latency as N/A. Its a rare edge case but still worth handling nicely.

windsock codebase

A quick walkthrough of the relevant bits of the windsock codebase:

• The bench implementation sends instances of the Report enum to windsock to keep it up to date with how the bench is going. In this PR, in the report.rs file, we replace Report::ConsumeCompleted with Report::ConsumeCompletedIn changing the way the user interacts with windsock to allow them to report consumer latency.
• There is also some logic for processing of Reports within windsock itself living within report.rs. This PR modifies this so that consumer latency is processed and stored in the final report.
• tables.rs takes a windsocks final reports and displays them as ascii tables in the console. In this PR we modify the table to include rows for consumer latency.

New table format

This is what the table output looks like now with consume latency: