Fix slot time error on bootstrap

[Neylix]

Description

If a node start just before a slot time and finish its bootstrap after the slot time, the first slot created will have a wrong slot_time ad causes this error during beacon summary :

Type of change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Add a Process.sleep() before starting bootstrap and run a node before a slot time (every 10 sec in dev mode).
It now do not fall in error during the beacon summary

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