fix(levm): for pre Berlin don't use floor cost modexp (#1675)

**Motivation**

This PR is for fixing the Ethereum Foundation Tests on the ModExp
precompile.

**Description**

When the `base_size` and `modulus_size` is Zero, there is an early
return to not make all the operations.
In the Berlin fork was introduced a floor for the gas cost. We were
returning this floor cost also for the previous forks to Berlin.
Now is only added after Berlin.

crates/vm/levm/src/precompiles.rs

@@ -306,7 +306,11 @@ pub fn modexp(
     );
 
     if base_size == U256::zero() && modulus_size == U256::zero() {
-        increase_precompile_consumed_gas(gas_for_call, MODEXP_STATIC_COST, consumed_gas)?;
+        // On Berlin or newer there is a floor cost for the modexp precompile
+        // On older versions in this return there is no cost added, see more https://eips.ethereum.org/EIPS/eip-2565
+        if spec_id >= SpecId::BERLIN {
+            increase_precompile_consumed_gas(gas_for_call, MODEXP_STATIC_COST, consumed_gas)?;
+        }
         return Ok(Bytes::new());
     }