feat: optimize and delay even more fallback rpcs for blockhash

[FedericoAmura]

Description

This PR delayes even more the blockhash sync (#727) when using fallback rpcs (from 1 block behind to 30) to ensure that nodes will be able to verify it. Nodes accept up to a month old blockhash and the indexer service re-loops every 5 minutes. Being 30 blocks behind 6 minutes we ensure the blockhash/nonce used in session sigs will be validated by the nodes

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• Updated lit core unit tests
• Manually on local

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my 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