kernel/sequencer: process Sequence and message

Context

The Sequence message contains two fields, the number of messages to be included from the delayed inbox, and the messages sent to the sequencer.

When this message is received, messages from the delayed inbox has be returned to the user kernel and then the messages from the sequencer has to be returned too.

The idea of this merge request is to create a pending-queue. When a Sequence message is received, delayed message are transfered from the delayed inbox to this queue. Messages from the sequencer are added just after.

Then when the sequencer kernel has processed all the shared inbox, it will pop one message from the pending-queue and return it to the user kernel.

This solution allow the user kernel to reboot between two messages in the same sequence. It also allow the kernel to not process the totality of the "pending-queue" in the same level.

Previous MR: !9082 (merged) Next MR: !9230 (closed)

Manually testing the MR

cd src/kernel_sequencer
make test

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR