Fix timeout issue in subset making genserver crash + refactor

[Neylix]

Description

• Removed useless p2p view request while adding new attestation in subset
• Refactor p2p view creation
• Create slot and summary inside async Task to not block the subset Genserver
• Also fixes an old issue to send beacon slot even if not beacon slot node

Fixes #981

Type of change

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

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