Test for ICMP class

Added payload_provider module, prepared the structure for the executor
that will launch pings.

Now responses can be represented as human-readable, stastistics automatically update

Response now understands if the received message is an Echo Reply or a Destination Unreachable message. In the latter, it returns information about the error code. Optimized the succes property.
The Destination Unreachable messages are still untested.

Added full test coverage for payload_provider and utils modules

Implemented the logic of sequence number (still unverified)

Completed tests for the Executor module

Restructure responses

Ping function now relies on executor

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