Verification of `eth_getBlockNumber` for prover should not forward request

### Describe the bug

Currently we documented that `eth_blockNumber` will be forwarded to EL. This may cause to return the wrong block number which is not synced with the light client.

### Expected behavior

Return the latest block number signed by the current sync-committee.

### Steps to reproduce

_No response_

### Additional context

_No response_

### Operating system

Linux

### Lodestar version or commit hash

1.9.x

No files or tests are named. Start by tracing how the prover handles eth_blockNumber and eth_getBlockNumber, then identify where the response is forwarded to the execution layer. Done means the returned value is the latest block number signed by the current sync committee rather than an unsynchronized execution-layer value.

Written by the indexing model from the issue text.