Replace unsafe on-chain data sync in fast_sync with a canonical approach

[grishasobol]

What is broken?
ethexe/service/src/fast_sync.rs line 615 reads on-chain data from predecessor blocks without synchronization. This is an acknowledged unsafe workaround needed to pass events from predecessor blocks to ethexe-compute.

Expected behavior
On-chain data is read through a safe, canonical mechanism.

Actual behavior
Data is read unsafely from predecessor blocks as a temporary workaround.

Additional context
TODO: // TODO: unsafe solution - we need it for taking events from predecessor blocks in ethexe-compute. A canonical replacement is required.

[grishasobol]

@claude opus, whether this task make sense if #5425 would be committed ?