Fix committed offset is always behind the real offset by 1

[shamanu4]

Description

This PR fixes a bug, that committed offset is always less than log-end-offset in Kafka by 1 when all messages were processed. This bug causes 2 problems:

• after the worker restart, the last message from the topic partition was re-send to the consumer. (Was fixed by this check in the _drain_messages function: if committed is None or offset > committed. )
• if there was an offset reset in the partition to the latest, consumer lag is equal to 0. The next message that appears in this partition will be ignored by the consumer due to the previous check, in the _drain_messages function.

This PR increases any committing offset by 1, so the log-end-offset will be equal to 0 when all messages are read.

Fixes #34

[codecov-io]

Codecov Report

Merging #33 (361b09d) into master (7493b6e) will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master      #33   +/-   ##
=======================================
  Coverage   63.96%   63.96%           
=======================================
  Files          99       99           
  Lines       10272    10272           
  Branches     1153     1153           
=======================================
  Hits         6570     6570           
  Misses       3547     3547           
  Partials      155      155           

Impacted Files	Coverage Δ
faust/transport/consumer.py	40.22% <0.00%> (ø)

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[patkivikram]

Can you please rebase your branch?

[shamanu4]

Can you please rebase your branch?

Done