Better p2p concurrency

[ghost]

Description

Improve the P2P concurrency.
Before, back pressure pipelines were spawn for each TCP connection to control concurrency.
Now we want a more global back pressure and concurrency control, hence the pipeline is defined globally.
Also, I increased the nb of workers to avoid blockages when some processes are busy.

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[Neylix]

There is an error when running mix test