Verify prev block root in the executor and not only in the importer

[rymnc]

https://github.com/FuelLabs/fuel-core/blob/926b50bcb70ecf3f5ba6acc984a01d4be16bb1c4/crates/services/consensus_module/src/block_verifier.rs#L52-L73

defines the verify_block_fields function that is ran whenever a block is imported by a validator/node. We want to include this verification in the executor as well.

[Rustix69]

@rymnc Can I pick up this issue and work on ??