Follow-up of epoch-aware light client

[alxiong]

This issue tracks all the follow-up tasks spawn from the large PR: #2706

Related original issues: #2142, #2684

Besides the Sub-issues, other items:

• [ ] use shared types in sol_types::* and remove all unsafe transmute after https://github.com/foundry-rs/foundry/issues/10153 is merged
• [ ] (low-priority) #2556

cc @sveitser