Dynamic send

[allevo]

This PR implements a new method to send a message:

• batch_send follows the same flow as send
• every message is queued on a dedicated Tokio task and sent asynchronously
• if the internal producer is closed, the task stops to send
• remove batch_publishing_delay params (breaking)
• put integration tests under tests to avoid parallel execution. Parallel execution causes problems running the tests locally due to the limitation of the OS file description number.

I introduced also a bin to calculate the latency performance to proof the improvement on low send rate. The bin creates a producer and a consumer. Every minute, 50 messages with the current timestamp are sent to RabbitMQ and the consumer store the metric. Every minute, a log is printed with the statistics.

Before this PR:

$ cargo run --release --bin perf-producer
stats: Stats { average_latency: 59.54067, messages_received: 3000 }
stats: Stats { average_latency: 62.840668, messages_received: 3000 }
stats: Stats { average_latency: 58.391335, messages_received: 3000 }
stats: Stats { average_latency: 58.668335, messages_received: 3000 }

After this PR:

$ cargo run --release --bin perf-producer
stats: Stats { average_latency: 5.1963334, messages_received: 3000 }
stats: Stats { average_latency: 5.195667, messages_received: 3000 }
stats: Stats { average_latency: 5.288, messages_received: 3000 }
stats: Stats { average_latency: 5.148667, messages_received: 3000 }

[codecov]

Codecov Report

Attention: Patch coverage is 17.54386% with 141 lines in your changes missing coverage. Please review.

Project coverage is 88.85%. Comparing base (be36db2) to head (e171dcc).

Files with missing lines	Patch %	Lines
src/bin/perf-producer.rs	0.00%	132 Missing ⚠️
src/producer.rs	78.94%	8 Missing ⚠️
src/client/mod.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #276      +/-   ##
==========================================
- Coverage   90.17%   88.85%   -1.32%     
==========================================
  Files          80       81       +1     
  Lines        7390     7504     +114     
==========================================
+ Hits         6664     6668       +4     
- Misses        726      836     +110     

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