fix: decrease lighthouse mev --prepare-payload-lookahead from 12 to 8s (#904)

As currently used on pectra devnet-6

More context: https://github.com/ethpandaops/pectra-devnets/pull/79

src/package_io/input_parser.star

@@ -1342,7 +1342,7 @@ def enrich_mev_extra_params(parsed_arguments_dict, mev_prefix, mev_port, mev_typ
                 "cl_extra_params": [
                     "--always-prepare-payload",
                     "--prepare-payload-lookahead",
-                    "12000",
+                    "8000",
                     "--disable-peer-scoring",
                 ],
                 "el_extra_params": parsed_arguments_dict["mev_params"][
@@ -1368,7 +1368,7 @@ def enrich_mev_extra_params(parsed_arguments_dict, mev_prefix, mev_port, mev_typ
                 "cl_extra_params": [
                     "--always-prepare-payload",
                     "--prepare-payload-lookahead",
-                    "12000",
+                    "8000",
                     "--disable-peer-scoring",
                 ],
                 "el_extra_params": parsed_arguments_dict["mev_params"][